3D C++ Game Engine - yet another open source game engine - nem0/LumixEngine

Build engine port backed by GZDoom tech. Currently supports Duke Nukem 3D, Blood, Shadow Warrior, Redneck Rampage and Powerslave/Exhumed. - ZDoom/Raze

Classic point and click adventure game engine and editor - bladecoder/bladecoder-adventure-engine: Classic point and click adventure game engine and editor

Cheat Engine. A development environment focused on modding

A prototype of a pseudo 3d-engine made in Bash