Depends on your programming skills. Freespace is already open source, but for my money WCSaga still doesn't *feel* like Wing Commander, but rather Freespace with a Wing Commander skin. Prophecy has limitations, and isn't much to look at it - but it is authentic. I've not gone hands on with amazons new engine. Discussing it as I was told about it (can anyone confirm) whilst it's largely CryEngine under the hood the gameplay side of code is a component based system (increasingly the standard). Without playing around with it it's difficult to estimate the overheads. Unity is absurdly and unforgivably slow, but less so on PC and not so much that you can't recreate a 20 year old experience (they just remade Homeworld in it). It uses the same geomerics graphics tech as Unreal, the same physics engine, but is generally quicker to prototype in. The personal edition is free. As AD says, the advantage of the third party engines is their ability to be turned to almost any genre, so if not a space combat game that's the obvious choice. For space combat - knocking out a proof of concept is easy in any engine, but the time you'll spend recreating fundamental wing commander requirements, mission flow, AI - I'm not sure it's worth it.