The Nebula Device is an open source 3D game and visualisation engine written by the now defunct Radon Labs.It has support for scripting languages (e.g. Tcl, Lua, Python).It is available for download at SourceForge. The binary distribution comes with customized interpreters with built-in 3d capabilities, and some demos.Try it out... it's impressive.
Nebula Device uses a special version of Tcl (MicroTcl). It is reduced to 36 commands for 160 Kbytes.
dbohdan 2014-12-26: The the original creator of Nebula Device has launched a new experimental cross-platform C++ game engine called Oryol. It has no support for Tcl or other scripting languages yet AFAICT.
m-nebula - medical graphic engine (also still be a game engine) used in therapeutic systems. Modification of Nebula1 game engine, originated by Radon Labs GmbH and continued and modified by InSightec Inc. Script support: Tcl and Python.