Purp - A smart to-do list and goal tracker app
Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Nirow - Habit tracking: Automated, Siri-ed, Calendar-ed, and More!
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
Things - Things is an easy to use task manager.
Quest - Quest lets you create sophisticated text-based games, without having to program.