orciencor has given the CORRECT locations for maps(to show up in the galaxyforge page) made with the included in steamapps\sin rebellion\galaxyforge galaxyforge.exe, but if you attempt to load a map made with the downloaded galaxyforge3 from the downloads page in rebellion rebellion WILL CRASH to DESKTOP since rebellion v1.02 no longer knows HOW to correctly read maps fro the older galaxyforge.
there is a couple of map updating tools to convert maps from older map formats to the current sins/rebellion formats and both are still in development ie still being improved/made more reliable.
harpo