http://aurora2.pentarch.org/index.php
Aurora is my favorite Sci-Fi game, and in some ways it's got lots in common with Limit Theory. It got a pretty endless universe (1000 planetary systems or more to explore if you want). It also has a working economy, in the sense that all ships are made up from mined raw material, either from asteroids, comets, moons or planets.
Aurora is also designed by one single dedicated programmer.
In other ways it's the opposite of LT, Aurora has no 3d graphics (and hardly and 2d either)! Pretty much like a Dwarf Fortress but in space. Most of your game time will be spent staring down datasheets. Aurora is also a management strategy game, not about flying around in space yourself at all.
What it does have is a very cool system to design your own starships and navies that I hope LT can learn some from. Designing a starship in Aurora is truly an art of real engineering skills.
The big point that I love about Aurora is that everything with ship design is a tradeoff. You have to carefully distribute weight over components like engines, armor, weapons, shields, sensors, magazines, fuel, living quarters (to gain mission time) or engineering (to gain maintainence life) and many more. Further you tailor most components to your needs, sensors specialized in detecting missiles, small ships or large ships. Engines can be tailored to provide very high power at the cost of many times higher fuel consumtion. Weapons, missiles and launchers can be specialized too.
Do you want a slow missile that can be launched from huge range or one with extreme speeds that's almost impossible to shoot down but has to be launched from very close?
Do you want a few really big guns that fire slowly or many smaller guns that lack range and power but fire silly amounts of rounds?
Do you want a few launchers that can spit out missiles from your magazines at incredible rate, or 6 times as many launcher racks that can't be reloaded until your back at base?
Do you want a ship with high speed or one with loads of armor? Or why not have both but compromize in less weapon loadout and range?
Do you want a dedicated sensor ship in your fleet or distribute sensors on all ships for flexibility and redundancy? Without sensors your almost blind until something is ontop of you.
With a system like this you will try and fail many many times before designing a competetive ship, but that's all part of the fun
It sounds awefully complex (and in Aurora it also is) but it doesn't have to be.
Two very user friendly sliders could define an engine, one for it's size and one for it's efficiency vs power.
The same with guns. With sliders you could very easilly budget how much of the weight is distributed on barrel length (accuracy and armor piercing), barrel caliber (damage), turret gear (tracking speed) and reloading mechanics/cooling (firing speed).
Armor is simply a slider that adds to ship weight on top of everything else and slows down speed and manouverability as a result.
In Terminus, you could do all the bread-and-butter stuff of open world space sims: dock, use warp gates, trade, take missions, etc. It was also quite "realistic" (as space games go) - you have to concern yourself with fuel, oxygen, power supply, and even radiation from your own reactor! And the way you design your ship will decide if you will have enough of those things. You could design the aesthetics of your ships, choosing different modules and changing their size, position, rotation and color. You could also choose what capacity nuclear reactor to use, what engines, weapons etc.
The crazy cool thing about Terminus' ship design was that it gave you a ton of freedom - so much freedom your designs could fail, in fact! I once built a ship I expected to be awesome - it had super powerful engines, plenty of weapons, etc. But when I launched from the station, it quickly became apparent that the reactor I added was too small and cheap, and the power supply quickly dropped. Thankfully, I was able to turn the ship around and get it flying toward the docking bay again before power totally died - and I was able to drift into the station (Newtonian physics) before I ran out of oxygen (O2 pumps die when the power does)!