OpenRCT2 seems to be doing pretty well regardless. I don't know how the player counts compare, but the OpenRCT2 community seems very active and the engine seem

OpenRCT2 seems to be doing pretty well regardless. I don't know how the player counts compare, but the OpenRCT2 community seems very active and the engine seems to have a good deal of care and polish put into it. They upgraded the file format a while ago, greatly expanding the capabilities of the game (increased ride limit, etc)