fheroes2 is a recreation of Heroes of Might and Magic II game engine
Magic Another Game Engine
Engo is an open-source 2D game engine written in Go
Go 3D Game Engine
Opensource Game Studio
Real-time RPG for PC/tablet/phone; multiple quests and random dungeons
Game engine for playing tomb raider 1 - 5 levels.
Intrinsic is a Vulkan based cross-platform game and rendering engine
Mahasona engine is an open source game engine.