fheroes2 is a recreation of Heroes of Might and Magic II game engine
The ioquake3 community effort to continue supporting/developing id's
dhewm 3 main repository
LayaAir is an open-source 2D/3D engine
All-in-one game engine built on Godot. Roblox & UEFN alternative
Descent 3 by Outrage Entertainment
Injectable LUA scripting system, SDK generator, live property editor
A PICO-8 demake of the SCUMM engine
An open source re-implementation of Diablo 2