Learning how to make custom PCBs and 3d printing. I really like Radio Taiso (daily calisthenics synced with music), so I made a dedicated speaker (https://www.taisospkr.com). It was fun to add new tools to my tool belt (ESP32, remote firmware updates, embedded website, streamlined wifi setup). Already have a new project based on a very similar architecture that I'm super excited about! Making PCBs and hardware has never been easier as a solo developer.