well, the thing is Anim8or is going to be released with a much empowered animation system. basicly addition of IK and vertex mapping.
Character Fx (15$) is not free, but imho has better features for animation.
3d canvas has a version for 34 $... I think it exports directx with weights in that version.
Blender is free. And is in the proccess of getting a directx 8 exporter full with bones and weights animation export. Lately things are moving quick in that field: there's been released a working md2 importer/exporter for Blender, and in the works now a md3 importer/exporter.Blender is hard to learn, but for those with enough patience, it can get to be a very complete thing for games.
Anim8or yet don't have individual vertex weighting. You only can use envelopes. That avoids realistic human animation.
Also, the format and internal stuff may change a lot. And the new anim8or version could be here in some months, (is what I suspect) Who knows if sooner.
I have a friend, very good coder, experienced a lot in export import 3d formats, and told me it'd not be possible to do an animation code for Anim8or with the available info about the format and stuff. Though there's a format txt out there, seems is not enough for making the animation code.
The author seem not to like of people tallking bout sharing the anim8or code -and he is in his rights if he wants so- so...
btw, there are other animation features, like joint pinning (available in Art Of Illussion, like IK also, and vertex mapping) that aren't neither in Anim8or (but could be in the next version) neither in Character Fx. And it's also way hard to animate so, and inaccurate. AOI and Blender have it. AOI though, is way easier to handle. There could come a directx8 exporter for AOI done with the scripting that it has -also, is open source- so, that probably would be the very best option for any artist. I'd prefer also to have the exporter done in Blender, but that's already being working out...hmmm..if some good coder here wanna give a try to a dx8 animated export format for AOI...

the key is being able to export bones, weights per vertices, and animation...
aoi.sourceforge.net