HAP is a homological algebra library for use with the GAP computer algebra system, and is still under development. The current version 1.25 was released on 25 January 2020.
The initial focus of the library was on computations related to the cohomology of finite and infinite groups, with particular emphasis on integral coefficients. The focus has since broadened to include Steenrod algebras of finite groups, Bredon homology, and general computations in algebraic topology relating to finite CW-complexes, covering spaces, knots, knotted surfaces, and topics such as persitent homology arising in topological data analysis. This tutorial table of contents gives an indication of topics covered. This book provides a detailed overview.
A list of some papers which refer to HAP can be found here.