LÖVE, also known as love2d, is a free, open-source game development framework based on Lua and SDL. It is intended to be easy to learn and cross-platform, with official support for Linux, macOS, and Windows, and there also exist ports to Android, iOS, and others. There are also experimental build-for-web versions such as love.js.
It is primarily oriented around 2D games, although with its support for luajit FFI it is possible to make calls directly to the underlying OpenGL context; this has been used by a handful of games. There are a few 3D engines : g3d, 3DreamEngine, Quinta3d (self-described 'The World Worst 3D Engine!!!'). There's also LÖVR, which is designed specifically for 3D games and VR.