ASSIMP currently supports the following file formats (note that some loaders lack some features of their formats because some file formats contain data not supported by ASSIMP, some stuff would require so much conversion work that it has not been implemented yet and some (most ...) formats lack proper specifications):
Collada ( *.dae;*.xml )
Biovision BVH ( *.bvh )
3D Studio Max 3DS ( *.3ds )
3D Studio Max ASE ( *.ase )
Wavefront Object ( *.obj )
Stanford Polygon Library ( *.ply )
AutoCAD DXF ( *.dxf ) 2
Neutral File Format ( *.nff )
Sense8 WorldToolkit ( *.nff )
Valve Model ( *.smd,*.vta ) 3
Quake I ( *.mdl )
Quake II ( *.md2 )
Quake III ( *.md3 )
RtCW ( *.mdc )
Doom 3 ( *.md5mesh;*.md5anim;*.md5camera )
DirectX X ( *.x ).
Quick3D ( *.q3o;*q3s ).
Raw Triangles ( *.raw ).
AC3D ( *.ac ).
Stereolithography ( *.stl ).
Autodesk DXF ( *.dxf ).
Irrlicht Mesh ( *.irrmesh;*.xml ).
Irrlicht Scene ( *.irr;*.xml ).
Object File Format ( *.off ).
Terragen Terrain ( *.ter )
3D GameStudio Model ( *.mdl )
3D GameStudio Terrain ( *.hmp )
Ogre (*.mesh.xml, *.skeleton.xml, *.material)3
Milkshape 3D ( *.ms3d )
LightWave Model ( *.lwo )
LightWave Scene ( *.lws )
Modo Model ( *.lxo )
CharacterStudio Motion ( *.csm )
Stanford Ply ( *.ply )
TrueSpace ( *.cob, *.scn )
See the Importer Notes Page for informations, what a specific importer can do and what not. Note that although this paper claims to be the official documentation, http://assimp.sourceforge.net/main_features_formats.html
3: These formats support animations, but ASSIMP doesn't yet support them (or they're buggy)
ASSIMP is independent of the Operating System by nature, providing a C++ interface for easy integration with game engines and a C interface to allow bindings to other programming languages. At the moment the library runs on any little-endian platform including X86/Windows/Linux/Mac and X64/Windows/Linux/Mac. Special attention was paid to keep the library as free as possible from dependencies.
Big endian systems such as PPC-Macs or PPC-Linux systems are not officially supported at the moment. However, most formats handle the required endian conversion correctly, so large parts of the library should work.
The ASSIMP linker library and viewer application are provided under the BSD 3-clause license. This basically means that you are free to use it in open- or closed-source projects, for commercial or non-commercial purposes as you like as long as you retain the license informations and take own responsibility for what you do with it. For details see the LICENSE file.
You can find test models for almost all formats in the <assimp_root>/test/models directory. Beware, they're *free*, but not all of them are *open-source*. If there's an accompagning '<file>.txt' file don't forget to read it.