An implementation of G.R. into unity. Use it however you like (and give me some credit :>)
The Kerr metric, with a spin parameter near to 1.
A spherical universe, with local object interaction.
Interior geodesics in the Kerr-Schild metric, with its horizons.
And more! The only things left to be implemented are for example, solving Einstein's field equations. (However this will not be worked on as of yet).