Twine is, in the dev's own words, »an open-source tool for telling interactive, nonlinear stories«. Recently, there was a great story on the new york times on the atypical games that are made using twine, and how twine enables (or empowers) games dealing with themes and topics that usually have no chance in the industry:
http://www.nytimes.com/2014/11/23/magazine/twine-the-video-game-technology-for-all.html?_r=0
