Coldest

What file format are the models for the mechs using, as well as other objects in the game?

It's custom, but there is a script for converting from .obj files.  It's just called convert and it should be in the Git repo.  I found a bug in it the last time I used it, but I think that should be fixed now.

It's a bit complex to use so you might want to take a look at some of the commands I've used for existing files.  I'm not sure they all include them, but if you look at a file like coldest/models/nemesis/legs/base you'll see the convert commands I used at the bottom.  For that one there are two since the legs have both a running animation and a standing frame.

There are also .matmap files that are used to map the .obj material to a Coldest material, and there are a few of those in the model folders too.  Since most of the models are a single material those tend to be one line files.

The whole art pipeline is pretty fiddly right now, so chances are you'll run into problems if you try to get a model converted.  Let me know if you do and I'll see if I can help.

Are the 'source' 3d models of all in-game models available?

I have them, but I haven't checked them into the Git repo because that would make it extremely large.  I could probably tar up all of my source art files and make them available though.