I did my own some time ago, and it can do Kerr black holes, too ;) No accretion disks, though, but should be possible to implement. https://github.com/fizyk20/

I did my own some time ago, and it can do Kerr black holes, too ;) No accretion disks, though, but should be possible to implement. https://github.com/fizyk20/gr-raytracer https://github.com/fizyk20/gr-raytracer