I like to build things—applications, but also actual things. Kerf Your Enthusiasm is, besides a lame attempt at a pun, something that kills two birds with one stone: it's an app I made, and it helps make more things when I do woodworking projects.
At its core, it does some annoying math that should be easy for someone with an MSc in Applied Math... but gets complicated when you grow up with the metric system and suddenly have to deal with imperial. Also, when you're cutting things and moving wood around, you start doubting your own brain and really need a second opinion.
It's very very simple, but you can take at it if you want here.