If a file format was designed for a certain game, would it be legal to use that format for other games? They might not mind if its a free game, but what if someone eventually made something they sold?
I think there's a specific license agreement for each format. I'm still looking for Quake III Arena End User License Agreement. As far as I've heard, MD2 and MD3 formats are free for use, but of course I'll be sure only when I'll read the EULA by myself