Doom

Doom 2 Horde mode via Odamex! Fight back the waves of hellspawn in a massive PvE multiplayer event! Doom 2 is necessary to play. Classic copies work but also available on Steam and GOG, and Odamex will detect your copies of Doom and do all of the modding work for you. Download the Odamex Launcher here https://github.com/odamex/odx/releases/tag/v0.4.1