I enjoyed recently running a crossover event in a SW Necessary Evil game I was running. In one episode I had the players encounter a strange military force that was sending scouting parties from a portal (Coalition forces). They eventually defeated the Coalition and rescued an ally who the Coalition had determined was a D-Bee and was planning on bringing back across the portal for "questioning".

And it looks like I'm going to get a chance to run an actual RIFTS campaign. So I'm looking forward to that.