The Warfare SDL Editor is under the GPL license - as such, you are free to tinker with it, customize it, make something entirely new based off it, and so on... as long as you don't try to profit from it (otherwise, contact me first). Currently, it runs off of QT 4.0, which means that it will run on Windows, Linux, Mac, or QT Embedded operating systems.
The objective is to write up a simple model editor to allow people to set up animations, script events (doors, cameras, so on), and a few other things relatively easily
I'm trying very hard not to try and re-invent the wheel. As such, I recommend you create your models in Maya or whatever other 3D model editor is supported and then use this to add the finishing touches. While I suppose that there will be basic support that will allow you to create models entirely using this program, that is not the objective - there are much better tools out there for that.
The Warfare SDL Editor is currently in pre-alpha mode - it displays objects and lets you move the cameras around, but not a whole lot more as of yet
You can pick up the source code via subversion here (https://warfaresdl.com/svn/waredit). If you want to contribute, let me know and I will add you to the access list.