"AOL" and "open source" haven't typically been two phrases you'd utter in the same breath, but that may be changing. For two years now, AOL has been pushing a development named Open AIM that encourages developers to build clients for the AIM network. Now, with Open AIM 2.0, it has kicked things all the more open -- albeit with a few gotchas that will probably turn off people accustomed to more uninhibited development practices.
The single biggest change with Open AIM 2 is documentation for the OSCAR protocol, the proprietary network standard AOL developed for AIM which until now most people had to reverse engineer. It's a little like Microsoft and its handling of the Office binary file formats: for a long time it's been one of their most closely guarded secrets, available only to those who pay a licensing fee. There are many other changes, described in the link above (like the fact that you can now build multiple protocols into an open-AIM client), but I know this is the biggest and most crucial one for most of the people building third-party AIM clients.
Now come the gotchas in the licensing agreement. The single biggest gotcha is that for any client you build using the Open AIM toolkit, you have to include at least two of the following features: AIM Expressions, the AIM Toolbar, the AIM Start Page Launch option, Buddy Info, or ad windows that return revenue to AOL. Another gotcha: if you ever have more than 100,000 simultaneous users logging into the AIM service with your client, the ad service becomes mandatory (barring some kind of alternative agreement with AOL).
It's essentially a variety of the "badgeware" provision that I've seen in some other open source products (Zimbra and SugarCRM come to mind). This provision has generated controversy in the open source community as to whether or not such a thing really constitutes a valid OSI license. AOL's conditions -- which amount to a variety of enforced adware, under the circumstances I've described -- are likely to make the stauncher open source advocates howl with anger.
There's more. Among other things, developers get issued a series of application keys, called Open AIM Keys, which are used to register your client project with AOL -- which can be canceled at any time and for any reason. Oh, and "AOL is under no obligation to provide you with any error corrections, updates, upgrades, bug fixes and/or enhancements of the Tools."
If this sounds harsh, look who's providing all this. This is AOL, which makes a fair chunk of its money leasing ad space through its software in the first place. It's a little naive to expect them to abandon one of the few business models left for a company of their ilk. Nice of them to take a step in the right direction, though -- people just need to be aware what kind of strings are attached, if they choose to play along at all.