In October 2009 I started a project called and a month later announced it. I talked about how it will bring notifications to the web. Now that it’s basically alpha complete, I’ll give you a quick walkthrough of what makes it so great.

At a really high level, you can think of as a notification router. As a web service, it provides a singleton endpoint for any web-connected program, whether a web application, desktop application or user script, to send notifications to somebody. For users, you can control what notifications you get and how you get them. In this way, is like a global, web-accessable version of the popular Growl application for OS X (which should honestly just ship with OS X). Only it’s even better.

Desktop Notifications
The original inspiration for was to make Growl more useful by fixing its ability to receive notifications from the Internet. Out of the box, Growl is effectively only good for notifications from sources running on your machine. If you wanted to get notifications from a web app, you’d have to wait for them to release a desktop notifier, which hopefully would use Growl to actually display the notifications. So you end up with all these desktop notifiers running for some apps, and have no option of desktop notifications for others.

This is probably the killer feature of it lets you get desktop notifications from any web app that supports it, which is an order of magnatude easier for them to do than build their own desktop notifier.

Sources and Outlets
The language of is based around Sources and Outlets. Sources are pretty straightforward. They’re a source of notifications. They could represent an application, script, company, person (or perhaps object?) that can send you notifications.

Outlets repesent the other major feature of They’re ways you can get a notification. The Desktop Notifier is your first and default outlet, but is just one of several options. Currently supported Outlets besides Desktop Notifier are Email, Jabber IM, and Webhooks. Outlets to look forward to are SMS, Twitter, IRC, and perhaps telephone.

The magic is in routing notifications from Sources to Outlets. Currently this is a simple mapping of Source to Outlet. For example, you can get notifications from Source A on your desktop, while notifications from Source B go to IM. This simplistic routing is just the beginning. We’ll talk about how we’ll do advanced routing when we get to the Roadmap.

The Nio Client
For developers, it’s worth mentioning that the pipe for our Desktop Notifier is really just a Comet HTTP stream. It can be consumed by pretty much anything. We were originally talking with Growl and authors of other desktop notifiers of direct integration. This is still a possibility, but just so we could move forward, we built our own client for OS X. Clients for other systems are available (but not yet “officially” supported) or are in progress, including Windows and Android.

Our OS X client is called Nio, short for, so you can pronounce it N-I-O, but I tend to pronounce it “neo”. It’s basically just an application that sits in your menu bar listening to HTTP streams (yes, plural) for notifications and pipes them into Growl.

For ease of installing streams, we made it handle files of the extension ListenURL. Once Nio is installed, you can download a ListenURL file containing a URL and it gets installed by Nio. The URL we give you is basically a “capability URL” or secret URL. This means streams are not super secure, but this is by design. If you wanted, you could share your URL with somebody so you both get notifications sent to that Outlet. You can always delete the Outlet and make another to disable that URL.

The other cool thing about our client is that it has a shell script notification hook. This means you can have notifications trigger a shell script that’s passed the notification details. This is pretty powerful because it means you can do things like create your own local logging, hear your notifications with text-to-speech, or make certain notifications trigger a more obstrusive means of notifying you, such as Quicksilver’s Large Type feature. This kind of programmability is central to our approach to design, as you’ll see later on in the Roadmap.

Simple API and Approval Model
For proper adoption, we need web apps to integrate, so we have a super simple API for Sources. It’s a simple REST API based on an endpoint constructed by the target of your notification. Like Gravatar, we use an MD5 hash of a user’s email address to identify targets. For example, to send a notification to, you’d do an HTTP POST to this URL:

You’d pass a few parameters, with at least your API key (meaning you need an account) and the text you want to send, and optionally an icon URL, link URL, title text and whether the notification should be “sticky”. That’s it. The request should respond immediately so it may be quick enough to be done inline in your app, but we recommend it be done asynchronously.

Then what happens is the first notification you send actually triggers a notification to that user that you want to send them notifications. If they accept, future notifications will be sent and your previous notifications will show up in their history. This may change to replay previous notifications on approval, but the point here is the user has to approve notifications before they get them. In this way, it’s similar to Jabber’s approval model and helps avoid spammers.

Public Service Software and its clients are open source. The service is free. Or rather, it’s not-for-profit donationware. is being run under a model I’m developing called POSS, the goal of which is to automate/abstract away the maintainence and funding of its operation. The end result should be: the service exists, it’s open source, and some in the developer community can deploy changes. But no single person is financially responsible for it, and it’s run on maintained cloud infrastructure. In this case it’s mostly App Engine.

This means that is not a startup. It’s public infrastructure. Ideally, I’m not even in the loop. It should be a self-sustaining public service. This is not fully realized, but it will be as it starts to consume more resources. For more information, you can read more on POSS or join our discussion group.

For now, the important thing is that is open source. This means anybody can contribute bug fixes, new outlets, new desktop clients, etc.

Okay, sure, is pretty cool now. But here are some of the major things that will be coming soon. Hopefully with your help!

Advanced Routing and Filters
From the beginning, I wanted really powerful routing and filtering. My evangelism of webhooks has given me the obvious answer to this, but in a more integrated way. Basically, how do you allow any routing scheme imagineable by users? Let them write code. Originally it was going to be powered by Scriptlets, but since I split the eval engine out as DrEval, it will be based on that.

Basically, just a imagine a UI with a little textarea for writing JavaScript that can make web calls. Route notifications based on your IM status, your location, what music you’re listening to, arbitrary time schedules, or anything you can code.

More Outlets
Obviously, more Outlets are good. Obvious ones are IRC, SMS, and Twitter DM. With Twilio we can do voice call notifications. Integration with push clients like the iPhone’s Prowl app would be easy to do. Our outlet system is very simple, so you can look at the source of our existing ones, write an outlet and it’s likely we’ll deploy it.

OpenID Support
Right now, you authenticate with Google. I don’t believe in creating authentication systems, and Google was the quickest given the platform. It’s also pretty popular and ensures you have an email address we can use. However, there are plenty of people that don’t like the idea of using their Google Account, so at some point we’ll support OpenID login and then go from there.

Multiple Email Support
Ideally, a web app can use whatever email address you used to register with them to send you notifications. However, unless Gmail is your primary email you use for registration, they’ll still need to ask you for your email. It’s the Gravatar model. So like Gravatar, we’ll need to let you add multiple emails to your account, allowing web applications to be able to send notifications based on any of them.

Convenience Libraries
Our API is simple, but people are lazy. We’re currently working on convenience libraries for popular langauges that it make that much easier to integrate with If you use a neat language, you should make a libnio package for it!

Ad-hoc Sources
Sources require an account, which is a bit heavyweight. Sometimes you want to create your own distinct sources to share with others or use in your scripts to easily send yourself notifications. This is the idea of Ad-hoc Sources, inspired by David Reid and capability URLs. The idea is simple: create an ad-hoc source and you get a secret URL. This URL acts just like the notify API endpoint, only you don’t need an API key. You can use this in public scripts or give it to others to send you notifications, and if it’s ever abused or falls in the wrong hands, just delete it and make another.

More Supported Clients
A developer in Japan started a Windows client based on Nio that we’re planning to support as our primary Windows client. Another developer is working on an Android client. iPhone users have Prowl, so once there is a Prowl outlet, you can get them on your iPhone. But Prowl is not free, so perhaps it would be helpful if we had our own iPhone client. There are the beginnings of a Linux/libnotify client. These are all ways you can start contributing to ;)

That’s about it. You can probably see why I describe as the open notification platform of the web. It’s simple, powerful, and open source. It’s come a long way in just 3 months thanks to the contributions of Abimanyu Raja, Amanda Wixted, Mike Lundy, David Reid, Christopher Lobay, Hunter Gillane, Nakamatsu Shinji, and everybody that’s given user feedback so far. I recently made a quick screencast for the homepage that I’ll end with so you can see it in action.

I’ve been playing a lot with Comet lately. It started with, in which I decided to prove that HTTP streaming was a simpler alternative to XMPP in getting messages to the desktop. That went quite well, but it was easy because it wasn’t all that different from a socket connection. Then I built a yet-to-be-announced site that uses real-time updates, and I was forced to deal with Comet to the browser. That’s a bit more complicated.

Actually, I’m arguably a veteran of Comet in the browser. I was doing it before it had a name, all the way back in 2005. A friend and I were using it (without knowing that it was terribly novel) to build a real-time strategy game in the browser called AjaxWar. I haven’t really done a lot with it since, but I was hoping after almost 5 years there would be all kinds of advances in libraries and tricks that would make it super easy.

That was not really the case.

There are things, but not easy things. The Bayeux protocol? I guess all that would be easy to do if there were a lightweight Javascript library for it. But there isn’t really. There’s a jQuery one, but it’s completely undocumented. Plus I was just sitting there thinking, do I need all this? Handshaking? Message envelopes?

I was also hoping for actual persistent connections (that’s what we did in AjaxWar), but it turns out the standard today is long-polling. This is a semi-persistent connection that drops after every message and then reconnects and waits for the next message. I also wanted JSONP and cross-domain support. So I ended up using the dynamic script tag technique:

<script type="text/javascript">
	$(document).ready(function(){ waitForMsg(); });

	function waitForMsg() {
		$('body').append('\<script type="text/javascript" src="">\<\/script>');

	function gotMsg(msg) {
		// Do something with it

It’s fairly elegant in its simplicity and cross-browser support. But it has some weird side-effects that I’m not sure if any of the fancier systems got around. For one, it keeps the browser loading. While it’s waiting for messages, the browser says that page is still loading. I also ran into some issues where if I included, say, a Google Calendar widget on the page, it might not decide to keep the connection open (or even start it). I ended up putting a delay on the first call to waitForMsg() until after the calendar widget was likely loaded.

So it’s a bit brittle. You don’t know if it stops working. Therefore you can’t do retries. And you never know if you happen to miss a message between connections (unlikely, but something to worry about). Plus I think if you hit Escape it also kills it.

But this worked well enough for my projects. I knew that if I found a better way, I’d switch over to it, but it was good enough.


Then today I decided to solve the problem right once and for all with a project called CometCatchr.

CometCatchr a lightweight Flash component to be used by Javascript that gives you a persistent connection for Comet streams.

I know a very small number of people won’t agree with my approach using Flash, but I tend to be pragmatic. I trust Flash is generally available and the benefits completely outweigh everything else to me. It’s also not new. Even the Bayeux protocol includes Flash as supported connection type. Still, I couldn’t find any simple Flash component that gave me what I wanted.

CometCatchr gives me Javascript callbacks on messages, maintains a persistent connection across messages, retries on lost connections, works in all browsers, supports (participating) cross-domain message sources, and just freaking works.

It was a drop-in replacement to my previous technique that worked right out of the box:

<script type="text/javascript">
	function gotMsg(msg) {
		// Do something with it
<embed type="application/x-shockwave-flash" width="0" height="0" src="CometCatchr.swf?url="></embed>

It simplified my code, not just client-side, but now I don’t have to support JSONP callbacks on the server. CometCatchr also parses the JSON messages before passing the callback, so that’s taken care of too. I realize it seems less than ideal to couple this with JSON payloads, but I didn’t say it wasn’t an opinionated component.

In fact, it’s very opinionated. It likes single-line JSON messages sent via HTTP using chunked transfer encoding. That’s because that’s how I do Comet streams. Actually, that’s how Twitter does them, too. I’m quite alright with such constraints, but if you want to make changes, it’s MIT licensed and super simple to hack on.

So for the time being, I’ve more or less solved simple Comet to the browser, particularly for me. It also might be worth knowing that another motivation for building this component is that I intend to solve Comet and real-time stuff in the browser entirely… but uhh, yeah. Stay tuned.

The “real-time web” is a popular topic right now. My WebHooks initiative is both riding on this success and helping make it a reality. One sector of this trend is about notifications. Real-time notifications to you about events you care about.

For a long time we’ve had helper apps like the Google Notifier and more recently the Facebook Desktop Notifications app that bring events from the web to your desktop. Twitter has created a whole ecosystem of clients that not only let you actively check Twitter, but passively get updates from Twitter.

Simultaneously, we’ve had a bunch of systems like Growl emerge that give you a consistent, well-designed and customizable system for local applications to give you notifications. While your IM client is in the background, it can tell you somebody IM’d you and what they said in an unobtrusive way. It integrates with email applications to tell you of new emails. It gives any application developer a nice way to present notifications to the user in a way that’s in their control.

Some of the apps that bring web applications to your desktop like Tweetie, Google Notifier, etc will integrate with Growl (which has a counterpart on pretty much every platform, including the iPhone). The problem is that you only get these notifications when the desktop apps are running, despite the fact web apps are always running. And yes, you have to have an app running for each web application you use.

And that’s only if they built a desktop app and you were convinced to download it. Most web applications are never be able to notify you with any means other than email. But as I’ve argued before, notifications don’t belong in your inbox!

Another minor point is that all these apps use polling to get updates. In some cases this doesn’t matter, but as data starts moving in real-time, this batches your notifications into bursts that you may not be able to parse all at once. I use Tweetie to get Growl notifications from Twitter at the moment, and if a lot of people are updating, I get a huge screen of updates that I don’t have time to read before they disappear. It becomes useless.

A while back I attempted to make an app called Yapper that lets anybody send real-time notifications to your desktop via XMPP. It was an experiment, and ultimately not the answer. It was only part of the solution.

But today I’m announcing the full solution: a free, public, open-source web service called (Notify-I-O). integrates with Growl and other local notifiers (as well as email, Jabber, Twitter, and webhooks) and provides a dead-simple API for any web developer to send real-time notifications to their users.

You can think of as a web-level Growl system. It empowers users with a consistent, controllable way to get notifications, and it provides developers with a simple, consistent way for sending those notifications. is an open platform for notifications. It’s still in a pre-alpha state, but it already has several useful notification sources. Last Thursday I built Feed Notifier, which uses PubSubHubbub to give you real-time desktop notifications of Atom and RSS feed updates.

At SHDH 35 last Saturday, Abi Raja built a Facebook notification adapter for that’s yet to be released. And there a couple more in the pipeline (by me and others) to show the power of

Again, it’s pre-alpha, so before I talk much more about it, I should probably finish more of it. I just wanted to make sure I blogged about it in somewhat of a timely fashion. I seem to have a backlog of blog posts about apps I’ve built recently. However, is a pretty significant one. Feel free to check it out, just remember that despite its looks, it’s nowhere near finished — but it does work.