Last week, Blaine Cook congratulated me on Idavoll being in Apple Mac OS 10.6 Server, as its Notification Server. I did have contact with Apple's server team ages ago, about them using Idavoll and having added some customizatons, but never knew where it ended up. The list of Open Source projects used in Apple's products confirms the use of Idavoll, and Wokkel, too, as a dependency of Idavoll. Cool!
Idavoll, and thus Notification Server, is a generic XMPP publish-subscribe service, in Python with Twisted. Upon inspection of the code and the differences against the mentioned versions, most of the customizations match those I was already aware of: an SQLite backend, the whitelist node access model and associated member affiliations. The link to Notification Server at the open source list goes nowhere (yet), so I am unsure about the actual license of their additions. I contacted the server team, and will write again if I have more news on this.
At the nice post by Jack Moffitt on Apple's use of XMPP, Kael mentions the presence of more Publish-Subscribe goodness in Calendar Server. This is actually the stuff that uses Notification Server for push notification in iCal. As Jack says, it is truly great to see large corporations like Apple to embrace XMPP like this. I really wish Google Calendar had a similar feature. Now I only get meeting invites through e-mail. Apple's particular use of Publish-Subscribe reminds me of Joe Hildebrand's effort on WebDAV notifications, and I think that there are a lot of applications that could benefit from such push features.
As I touched upon earlier, at Mediamatic Lab, we use XMPP Publish-Subscribe for exchanging things for federation. But we've also built a bunch of interactive installations, most of them dealing with RFID tags we call ikTags. To name two examples, the ikCam takes a (group) picture, uploads it and friends the depicted persons by reading their tags. The ikPoll is a polling station where people can 'vote' on questions with the tag. Typically, there are also publish-subscribe notifications coming out of those interactions, so you can create a live stream of things happening at an event like PICNIC. Combined with the Twitter Streaming API and our own status messages, this creates an entertaining back channel, coincidently powered by Idavoll.