Name: The Eternity Engine
Website: https://github.com/team-eternity/eternity/releases
Status: Released
Release date: Nov 2, 2009
Availability: Free (provided a supported IWAD)
Name: PrBoom+/UMAPINFO
Website: https://github.com/coelckers/prboom-plus/releases/tag/v2.6um
Status: Release
Release Date: Jun 10, 2019
Availability: Free, provided you have the Doom IWADs