Blender3d

Blender therefore is fully free to use and distribute within any educational, professional or commercial environment.

Supported Platforms
Windows 98, ME, 2000 or XP
Mac OS X 10.2, 10.3, 10.4
Linux 2.2.5 i386
Linux 2.3.2 PPC
FreeBSD 5.3 i386
Irix 6.5 mips3
Solaris 2.8 sparc

Hardware
300 MHz CPU
128 MB Ram
20 MB free hard disk Space
1024 x 768 px Display with 16 bit color
3 Button Mouse
Open GL Graphic Card with 8 MB Ram

Offical Site