Aether is a 2D real time tactics game based on pure Newtonian physics. Fleets are constructed from 10 different ship hulls, which can be equipped with various specialized weapons, sensors, fighters, and other systems.
The player has intricate control over various ship systems, power management, repairing, etc. But the most important aspect of the game is managing the momentum and positions of the units to gain a situational advantage. The units do not have any maximum speed, and there is no fixed frame of reference.
It has computer opponents and networked multiplayer.
Something like a nebula that you could hide units in/around could be interesting. I don’t know about adding anything that the units could crash into though – the game has a pretty steep learning curve as it is without having to worry about that.