In addition we have all the sources to the tools they had developed to make Sonic Xtreme.
We have put together a full Saturn development environment and Nvidia NV1 PC to work with. As I said, we intend to build every revision and release every built binary we produce. Actually building this source is a pain, however, and these builds are glitchy. It'll take us time to build everything out, but we have some screenshots of current progress:

Level editor

Engine running on Saturn (well, SSF emulator, currently crashes on real hardware)
The engine we have includes builds as seen in these leaked videos from years ago:
https://www.youtube.com/watch?v=6IOd0mQ-uXE
You can follow our release progress in this thread: http://forums.sonicretro.org/index.php? ... 33545&st=0
Figured I'd drop a line....