Frontier Elite II was one of my favorites (still fire it up from time to time,
http://www.youtube.com/watch?v=hV_juoQvAbE&feature=share&list=UUKH06xroQsn7EOUHXeb7I0g), though my brother and I were talking about writing a similar type game using fractal math to generate star systems and such, were pretty in-depth about it. Neither of us had the coding skill to make it happen, though. Only mention it because one of the problems we couldn't figure out was how to handle "real" physics in an MMORPG setting. For just one player, hitting "fast-forward" to get the days/weeks required to transit from one planet or star system to the next isn't a problem, but trying to co-ordinate this accross several real-time players would require literally "future knowledge" of every players actions in the game. The best we could come up with was a universal time acceleration, which would compromise "reality" for maneuvering in local space. Gives me a headache just thinking about it.
Anyway, for multi-player support, one would need to scale back the realism a bit.
