It is external program, that runs Galaxy Editor and equip it with additional features transparently to end user.\ It is still in very early stage of development.
It creates new process for editor, perform a dll injection by process memory swap and wait for signals. Anything is controlled from external Lua script, what makes it very expandable. If you want more details or want to contribute, check source.
You can download latest build here, but be aware, it is not well tested and i can't guarantee it wont break your map. We don't have many compatible extensions for this moment too.
(aka scriptalter.exe) When you save your map, it adds additional trigger to MapScript. You should get "Gemini injection successful" message at third second of game time.