There is an OpenXT google group for information on existing development efforts. Feel free to join the group and discuss any / all aspects of the project. The use of these tools is subject to change in the future. If it turns out that (for instance) the Google Group doesn't work the way we want / need, we may expend the resources to set up an "old-school" mailing list. But for now, we're sticking to the free stuff. We also have an #openxt IRC channel set up on freenode. Feel free to join and ask questions there too.
The documents below are dated, especially with respect to video architecture, but may be useful to new developers. And fixing up these documents is one of the things on the task list mentioned above!