The active development branch of the Python-wrapped code can be found here:

https://github.com/21cmfast/21cmFAST

The previous, C-only version can be found at:

https://github.com/andreimesinger/21cmFAST

Please acknowledge the code by referencing the following papers:
Mesinger & Furlanetto (2007)
Mesinger, Furlanetto, & Cen (2011)