Star Ruler 2 is now Open Source:
http://starruler2.com/
I played the first one. It had a very innovative ship construction system that was pretty interesting. (I don't know how similar this version is to that one.) The 3d ship models were in .obj format, too, which made for easy modding. But, the caveat was that there was only one ship model... (Larger ships were just larger scaled versions of it.) There were also some interesting automation dynamics, too, which made parts of it similar to an X3 experience in how certain automated conditions worked, so that was nice. Planetary construction, buildings, etc, followed a progression and interaction system that was fairly bare-bones, to say the least, and one could load up an automated "Governor" priority list that basically min-maxed everything. Kinda not explored enough, IMO, and certainly a bit of a waste. The Tech Tree was an interesting sort of change compared to standard trees, but it was also a bit confusing.
But, it wasn't a bad game, really. The worst part of the overall design was, IMO, that combat was a sort of bullet-hell experience, with individual ships really not being significant, despite the really innovative design system. What that means is that the time you put into designing a great ship didn't really make that ship very significant in combat experiences you had with them. So, your "Impenetrable Gladiator Howitzer Blow-Up Righteous Defiance of the Gods" uber-cruiser was... just another blob on the screen. It wasn't the special little snowflake you spent a lot of time tweaking the design of.
Anyway, none of that matters - This is Star Ruler 2 and it's Open Source, so go have some fun with it if you want a sort of RTS 4X game.