UnGameEngines

UnAdventure Game Studio
UnAleph One
UnAllegro library
UnAngel2D
UnAnura
UnArdor3D
UnAxiom Engine
UnBlender
UnBuild engine
UnCafu Engine
UnClanLib
UnCocos2d, UnCocos2d-x, UnCocos2d-html5
UnConstruct Classic
UnCore3D
UnCrystal Space
UnCube
UnCube 2
UnDelta3D
UnDim3
UnDimensioneX Multiplayer Engine
UnDuality
UnENIGMA
UnEnv3D
UnExult
UnFLARE
UnFlexible Isometric Free Engine
UnFlixel
UnGame Closure
UnGameKit (OgreKit)
UnGamePlay3D
UnGamvas
UnGDevelop
UnGodot
UnGrit
UnHaaf's Game Engine (HGE)
UnHaxeFlixel
UnHGamer3D
UnHorde3D
UnHPL 1 engine
Unid Tech 1 (Doom)
Unid Tech 2 (Quake)
Unid Tech 2 (Quake II)
Unid Tech 3
Unid Tech 4
UnIndielib
Unioquake3
UnIwGame Engine
UnJake2
UnJGame
UnjMonkeyEngine
UnJogre
UnKivy
UnKiwi.js
UnKobold2D
UnLibGDX
UnLÖVE
UnMaratis
UnMinko
UnMoai SDK
UnMultiverse Foundation
UnNebula Device
UnNetGore
UnNME
UnNo Nonsense
UnnxPascal
UnOgre3D
UnONScripter
UnOpenClonk
UnOpenSimulator
UnORX
UnOxygine
UnPanda3D
UnParadox3D Game Engine
UnPixelLight
UnPlayCanvas
Unplayn
UnPolycode
UnPLIB
UnPyrogenesis
UnRen'Py
UnRoblox
UnRetribution Engine
UnSFML
UnSge2d
Unsmall3d
UnSpring
UnStarling Framework
UnStepMania
UnStratagus
UnTorque3D
UnTurbulenz
UnUrho3D
UnVanda Engine 1
UnWire3D
UnWorldForge
UnZenGL
UnZGameEditor

Why are you here?
https://twitter.com/cmuratori/status/575553648027176961