Okay, so here's some of the programs and file formats compatible with Biturn (and there are a lot).

3D Studio - ASC, 3DS

3DS Max ascii - ASE

Blitz 3D - B3D

HalfLife - MDL

Lightwave, Lightwave 6.5+ - LWO

Milkshape ascii - TXT

Milkshape - MS3D

Quake 1 model - MDL

Quake 2 model - MD2

Quake 3 model - MD3

Rhino - 3DM

SoftImage asci - XSI

TrueSpace - COB

This program is primarily used for extracting data from games. Unfortunately, however, it does not have direct support for Gmax (.gmax).