itch.io

Games which seek to lead the player on a journey through an uncertain and challenging world.

Science-fiction. Commonly including things like aliens, advanced technology, and settings of outer space or distant planets. 

Focused on using its text, moreso than its visuals or audio, to tell the bulk of its story/plot. (Still can have great audio and visuals, though!)

Twine is a free and open source tool for telling interactive, non-linear stories.