I haven't yet included a full list, but I guess I could include one.

All of those OSes you mentioned are included. BTRON isn't a single OS, but a small family of OSes based on a common specification (just like Unix is); the OS museum includes the demo 1B/V3 and Chokanji 4. The FOSS BTRON implementation you're thinking of is almost certainly B-free/EOTA, which is also included. EOTA never actually implemented BTRON proper before it got abandoned. It basically just ended up being like a Unix based on an ITRON kernel.

Documentation for some OSes is included, although I've focused more on user/administrator documentation over developer documentation. It would probably be a good idea to include developer documentation though.

I've thought about making individual images available for download, but many of them are dependent on particular emulator versions and/or the common launch scripts so it isn't quite that simple.