BallisticNG is a free Wipeout styled racing game on Steam currently in Early Access. It currently sits with very positive user reviews and has been praised for how accurate the physics are to the original Wipeout games.
The game can be modded, allowing you to import custom made ships and use a runtime track editor to create new layouts and playtest them instantly. This track editor is also the tool used to create the official tracks. The game can also compile and load c# assemblies, although it is not fully supported yet.