Greetings, fellow GM
I would like to point you out to this one
The interesting part is not the system (attached to it?) since all of you play RT.
But Starting with page 71 you get tools, tables and advice on building your own sandbox-style star sector.
This is of course not the re-invention of the wheel, but you have handy tables for names, descriptions for strange xenos creatures (although the "weird ones" are a little to...weird) an tables to roll up your whole biosphere and society.
And it is for free.
)