GameOn
OutyPlay
Axir
ChucK
Player.me
Smatchy
Teamy
Boulder Creator
Construct 2
Godot Engine
GDevelop
Unreal Engine
BYOND
Corona SDK
Defold Engine
Unity
GameOn
Construct 2OutyPlay - Join sports matches, create your own games and tournaments
Godot Engine - Feature-packed 2D and 3D open source game engine.
Axir - Need more active friends?
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
ChucK - A strongly-timed music programming language
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.