Because of my short attention span, and the fact that I usually do this stuff to learn a tool, some of these are half-finished or specific to my own use cases.
An event logging server using Django Channels and web sockets, designed for human input of low frequency events. It has a chat-bot front end that can be attached to Slack channels. Originally made to record my sneezes, along with possible causative events, to try to work out if there's a trigger. (I sneeze lots in the morning.) If you want to record a variety of mundane events, and you sit on slack all day, it works nicely.
A grounds-up re-implementation of the TeX programming language in Python. Not just the parser, or the output routines, or the math language, the whole thing. Because the original-and-still-current implementation from the 1980s is a mess (sorry Don).
A package for Sublime Text, to easily encrypt and decrypt files without leaving the editor.