Yep, Ca3DE (now known as the Cafu Engine) is yet another 3D game maker/engine by a German developer.

The earliest versions were for DOS, but Win32 OpenGL support was added in the early 2000s (about the same time as this snapshot of the official site), and eventually the DOS version was discontinued.

So far I've been unable to find any legacy releases of the demo. The engine has been continually developed over decades and it does not seem that an archive of old releases is maintained anywhere. Hallfiry's catalogue gave no results for "ca3d" or "ca3de" either. The DOS/Windows release from the early 2000s was supposedly in a zip file called CA3D.ZIP, which does not return useful results in Google or DuckDuckGo.