In this game I'm using the "Separate two objects", but it has some limitations (which instance is pushed is based on the order the objects were created). I sometimes use the Physics extension (with gravity set to 0) just to prevent things from overlapping or running through walls.
Viewing post in Extension: RTS-like unit selection comments
thanks for your answer. i use "seperate two objects" too, but it looks kinda 'unclean' (the units just pop up each other). when i give the units the Physics behaviour (with 0 gravity), only the first unit, which was created or set in the scene, moves - any other units can still be selected (i'am using your RTSlikeSelction extension) but don't move at all.