This is a project I started developing a while back that converts an Unreal T3D document to Quake's MAP format.
Please keep in mind that it's currently unfinished.
It currently only supports T3D documents generated by older versions of UnrealEd (e.g. 1/2).
There are a number of missing features and I haven't touched this in a while. Again, it's not finished.
It will convert all geometry and a number of actors, however much of the geometry won't be exported in a way you might expect due to the lack of rotation. It's also not as flexible as I would've liked.
If I suddenly find some time I hope to return to this again, but we'll see.