Gimbal is an indie game where you build your own spaceship and then test it in an arena versus other players in an on-line multiplayer match-up. The physics in this game are maybe 90% of the way there and I have one or two issues with the interface -- like not being able to zoom in on your ships or temporarily pull parts off your ship so you can see what you're doing.
However, the rest of the game is solid and I truly enjoyed myself. I even won a free-for-all deathmatch using a ship I built for $1.8 quadrillion -- chump change by the game's standards. When I think of this game, the phrase "nerd porn" springs to mind.
Currently, the developers -- 8888888 Games -- are looking for votes in the Greenlight section of Steam. I would recommend this game to anyone who likes to tinker with customization and enjoys working out the physics behind intra-stellar spaceship design. The game is currently on sale for $9.99 (regularly $14.99).