Children of a Dead Earth is a tactical space game with n-body Newtonian physics. This means that on the surface it is very similar to something like KSP, you can do things like orbit a Lagrange point. In addition, you can design all the parts of you spacecraft and weaponry down to the materials they use. If you can make a fuel tank made out of aerogel work with the laws of physics, then you can use it. For example, I made a coilgun that fires nukes which was devastating at close range but the low velocity of the nukes made them easy to dodge at long range and without any thrusters, they cannot course correct.
Olive is hardware accelerated and if pretty stable nowadays.