I maintain a fork of the Ott tool for programming language design. It’s highly experimental, so use at your own risk. The main modifications from the upstream version are improved error messages (machine readable with source locations), and expansion of the already-present Redex backend.
The beautiful Metropolis Beamer theme, modified to use the UBC Colors and Logo.
A small dependently-typed language, with an experimental unification algorithm for generating high-quality type error messages. Based on the research from my Master’s Thesis.