FREE GAME ENGINES! (feel free to edit and add more!)
- Ren'Py - the visual novel engine - http://www.renpy.org/
- Adventure Game Studio - the point-and-click game engine - http://www.adventuregamestudio.co.uk/
- 001 - the free graphical-scripting game-making engine - http://www.engine001.com/
- Unity - 3D professional game engine - https://unity3d.com/
- Stencyl - http://www.stencyl.com/ Make iOS (iPhone/iPad), Android, Flash, Windows & Mac games without code using Stencyl.
- Twine - interactive fiction engine - http://twinery.org/
- Quest - the text-adventure and interactive fiction engine - http://textadventures.co.uk/quest
- Inform - interactive fiction engine - http://inform7.com/
- Free RPG Engines: http://alternativeto.net/software/rpg-maker/
- ASEPRITE - /eɪs-praɪt/ — animated sprite editor & pixel art tool - http://www.aseprite.org/
- SFXR - an easy program that generates randomized sound assets for you! - http://www.drpetter.se/project_sfxr.html