HAP is a homological algebra library for use with the GAP computer algebra system, and is still under development. Its initial focus is on computations related to the cohomology of groups. Both finite and infinite groups are handled, with emphasis on integral coefficients.

It includes some functions for computing homology of crossed modules and simplicial groups, and also some functions for handling simplicial complexes, cubical complexes and regular CW-complexes in the context of topological data analysis.

It has been developed by Graham Ellis and colleagues in Galway.