We have a topic about industry standard 3d animation software, but I didn't find anything dedicated to FREE 3d animation software.
I will list only free 3d animation programs that at least theoretically can be used to animate characters in 3d.

So here I go:

Blender - the most popular free and open source 3d animation software.
OS: Linux, Windows
http://www.blender.org/

K-3D - is a free 3d animation software with procedural engine for all of it's content, making K-3D a very versatile and powerful package.
OS: GNU / Linux (stable), Win32 (stable), MacOSX (unstable), BSD (untested), Solaris (untested).
http://www.k-3d.org/

Anim8or - a free 3D modeling and character animation program.
OS:Windows NT4, Win95, Win98, WinSE, Win2K, or WinXP
http://www.anim8or.com/main/index.html

Cyberdelia - 3D Animation tool for Windows XP and Vista. Freeware.
OS: Windows XP and Vista
http://www.vixar.jp/cyberdelia/english.html

Art of Illusion - Java based free 3d Animation software.
OS: Any OS that has Java virtual machine installed
http://www.artofillusion.org/

Nice topic UVlas!
I didn't know about Cyberdelia.
Is it a good 3d animation software?

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Andyba, 3d artist
skills: 3d modeling, texturing, rendering, 3d character animation, compositing
3d software experience: 3ds max, Maya, Softimage XSI, Deep Paint 3d, Body Paint 3D, Wings 3D, Z Brush
2d software experience: Adobe Photoshop, Adobe After effects, Macromedia Flash, Freehand

Blender is very good program for 3d creating