Google Developer Day, not necessarily in that order, so I missed the announcements that Facebook had opened up their API.
As a software developer with a healthy affection for all things related to network effects and emergent behaviours, this is brilliant.
The applications provided get added to a central registry inside Facebook, from where you can pick and choose the ones you want added to your profile. They still have to be deployed separately (as Facebook doesn’t host them for you), but the user doesn’t see any of that - all of it is a very simple and well-designed UI, so “installing” an application to your profile is a hell of a lot easier than installing a desktop application to your machine, and gives the user instant feedback.
Leaving important considerations on data ownership and privacy aside, which I won’t comment on since I haven’t read the agreements in much detail, I can see this thing eating a huge chunk of what we nowadays use disconnected internet applications for. Instant, mobile and email-like messaging, discussion groups, photo sharing and some other basic kinds of applications are already there, as are little data aggregation tools, like the del.icio.us and Magnolia importers. If this API is successful (and so far, nothing suggests otherwise), other social networks could as well be dragged inside Facebook if they support any kind of external API. And, if not, there are always screen scraping tools like Hpricot.
Something to watch out for, definitely. Ten years ago, we were wondering what kinds of applications could be made to run on the internet. Facebook is making us wonder what kinds of applications can be made to run on top of a social network. Which ones would you try?