iOS

DOOM-iOS (C++, C, GPL-2.0, mature, inactive since 2012)
Esenthel Engine (C, C++, Custom, beta)
flixel-gdx (Java, 3-clause BSD, beta, inactive since 2017)
Game Editor (C, C++, GPL-3.0, mature, inactive since 2014)
GamePlay (C++, Apache-2.0, mature, inactive since 2016)
Gorillas (Objective-C, JavaScript, Java Research License, mature, inactive since 2014)
HaxePunk (Haxe, MIT, mature)
Hedgewars (Lua, C, C++, Pascal, Haskell, GPL-2.0, mature)
LÖVE (C++, zlib, mature)
NOVA PINBALL (Lua, GPL-3.0, beta, inactive since 2017)
OpenLara (C++, C, 2-clause BSD, mature)
osu! (C#, MIT, beta)
ouzel (C, C++, Objective-C, 2-clause BSD, beta)
Playir (C++, Apache-2.0, mature, inactive since 2014)
PyQt (C++, Python, GPL-3.0, Custom, mature)
Ren'Py (C, Python, Ren'Py, LGPL-2.1, mature)
Shattered Pixel Dungeon (Java, GPL-3.0, mature)
Simon Tatham's Portable Puzzle Collection (C, MIT, mature)
The Battle for Wesnoth (C, C++, Java, Python, Lua, GPL-2.0, mature)
Tux Paint (C, C++, GPL-2.0, beta)
Wagic, the Homebrew (C++, C, Objective-C, 3-clause BSD, beta)
Yet Another Engine (MoonScript, Java, Lua, MIT, beta, inactive since 2016)