21cmFAST
21cmFAST is the premiere semi-numerical 21cm cosmological simulator. It is currently used by every 21cm cosmology experiment to derive predictions of the spatial distribution of 21cm brightness temperature, to compare to observations.
I am a core developer in this project. My role has been primarily to wrap the fast C-code of the original simulator into Python, so that it can be more widely and easily used. This also has the benefit of adding a number of tests so that future development is safer and so that the code can be trusted by its many users.