My hobby is theoretical computer science, where I study algorithms, data structures, complexity theory and computational geometry.
Professionally, I freelance as a Ruby on Rails to develop small web apps that use or are based on spreadsheets for personal, small business or prototyping. Such as building a web app based on an excel document or importing data from google sheets. I'm currently working on a few such apps.
I've also previously done a bit of static front-end web development using using Jade/Stylus via the build tool, Brunch.io (NodeJS).