Engines and Distribution Tools

for visual novels

http://www.renpy.org/ - Ren'Py, dedicated VN engine
http://nscripter.insani.org/ - ONScripter, dedicated VN engine (translated version of NSCripter)
http://www.bladeengine.com - Blade, dedicated VN engine (only the light version is free, some nags)
http://www.visualnovelty.com/ - Novelty, WYSIWYG dedicated VN engine (still in beta mode)
http://www.studiomab.co.uk/Content.aspx/Sylph - Sylph, dedicated VN engine
http://bassnovel.com/ - BASS, online dedicated VN engine
http://visualnoveldai.com/novelstream - NovelStream, online dedicated VN engine
http://cs2.suki.jp/ - CatSystem2, Japanese only by the looks of it.

http://inform7.com/ - Inform 7 design system, greatly improved over Inform 6
http://www.inform-fiction.org/ - Inform 6, based on the Infocom format
http://www.adrift.org.uk/cgi/new/adrift.cgi - Adrift, needs Adrift Runner to play adventures
http://www.generalcoffee.com/hugo.html - Hugo, needs runner software to play adventures
http://www.textadventures.co.uk/quest/ - Quest, a text adventure engine that allows you to share your game online.

http://www.adventuregamestudio.co.uk/ - a free engine for making point-and-click classic adventures
http://www.adventuremaker.com/ - object-oriented adventure engine (only the light version is free)
http://www.gamemaker.nl/ - a free game-making engine (only the light version is free, some nags)
http://www.alice.org/ - a free game-making software

See this post for more freeware game engines, including RPG engines.

http://nsis.sourceforge.net/Download - NSIS, script-based install creator
http://www.jrsoftware.org/isinfo.php - Inno Setup, easier to use than NSIS but less powerful