My current project is Move by Numbers [0], a sort of "Twitch plays chess" type of game with a comfortable pace, points, and levels. The idea of cooperative gaming has intrigued me recently, and this is my first foray into the space. Building it has been entertaining, but finding users and gathering feedback has been a struggle. I'm learning first-hand how difficult marketing is.
I also just published an article on tracing 2D metaball outlines [1], so if you enjoy visual explanations of algorithms, check it out.
Up next on my list is either a declarative charting language and cross-language interpreters for said language (data visualization is something I worked with a lot in my previous job), or a Japanese grammar textbook I've been dreaming about writing for several years now.