HAP is a homological algebra library for use with the GAP computer algebra system, and is still under development. The current version 1.21 was released on 13 August 2019.

The initial focus was on computations related to the cohomology of finite and infinite groups, with particular emphasis on integral coefficients. The focus has now broadened to include coefficients over fields (Steenrod operations etc.) and computations in the context of topological data analysis (regular CW-complexes, persistent homology etc.). The table of contents gives an indication of topics covered. This book provides an alternative overview.

A list of some papers which refer to HAP can be found here.

Some functions rely on the deposited packages HAPcryst and Polymaking and on the package HAPcocyclic.