FAIM, or more appropriatly, libfaim, is a library used to access the AOL Instant Messenger service. Its been ported to various UNIXen as well as Win32. Several clients have used some incarnation of libfaim over the past year and a half: gtkFAIM is now a 100% dead project (because I discovered gtk hates me), gtkTTM never amounted to anything, naim has been around quite a long time and is again working with the newer libfaims, everybuddy now uses the TOC protocol instead (but is looking at using libfaim again), and the libfaim port of gaim is now fully operational.
Other than the functionality of the clients, libfaim is a useful source of AIM protocol information, as its far more up to date and most likely more comprehendable than the actual documentation I provide.
libfaim supports several of the modern features of the AIM protocol (in particular, chat), and has the infrastructure to support the majority of the others (its just a matter of doing it). Support for file transer and DirectIM is forthcomming.
In its current state, libfaim is very much a few-user, even-fewer-developer project. I make updates quite irratically and always on a mere whim. It often takes me days to write a single small feature and then get a huge feature done in less than a week (chat is a good example, for those people who know what I'm talking about). As such, the current version is available only in CVS. I used to make snapshots after big changes, but I seem to have fallen out of that habit (I haven't made a snapshot available since late 1999). Instructions for pulling down the latest tree from CVS are here.
2 jun 2000:As of today's CVS libfaim, its now possible to use libfaim to login to ICQ, thanks to AOL's merging of the services (as of ICQ2000a windows client, which does the same as libfaim). You can't talk between services yet (thats blocked by AOL), but if you login to ICQ you can join AIM chat rooms, which is one way of talking to AIM users. Have fun. (Most clients will work without even needing to be recompiled -- however, some others may need to send a higher client version in their client info at login to be able to use ICQ.) Also, the OSCAR (libfaim) port of gaim is active again and actually working this time.
19 mar 2000: Updated above. There's been great stuff happening to libfaim that has pretty much been hidden unless you're one of the "in" people.
Older/historical news can be found there.
For discussion of AIM/OSCAR protocol issues, there's the libfaim-aim-protocol list. For discussion of libfaim developement issues there's the libfaim-devel list. Instructions for subscribing to these lists are available here.