Since people are talking about dialog stuff this was just released.
http://www.secretlab.com.au/blog/2016/2/10/yarn-spinnerYarn Spinner
Complicated stories don't have to be complicated to build. We've already seen how Twine has made it easier than ever to create interactive fiction. Another tool, Yarn, has taken inspiration from Twine, and made it awesomely simple to craft interactive fiction.
This is where we come in. We also love telling stories, so we're absolutely delighted to introduce Yarn Spinner, an open source implementation of the Yarn language that's designed to make dialogue in your games a snap.
We built a tiny little demo game, which is set in space and available for you to play right now! It requires a keyboard to play it, and is compatible with most modern browsers.