Failbetter Games (
http://about.failbettergames.com/), the people who made the excellent browser-based story game Echo Bazaar/Fallen London, recently released their toolset ("StoryNexus":
http://www.storynexus.com/) in open beta for people to build their own story games with. And while it's a hosted application, they explicitly disclaim any ownership right to IP you create using StoryNexus, so you can build worlds there without worrying about problems taking the setting or characters to other media down the road.
Unfortunately, in my limited experiences with StoryNexus so far I have found it to be damn near incomprehensible to use. Hopefully they will clean up the interface and streamline the design process somewhat before calling it 1.0.
