Still learning them. This seems like a great book for that.
Compiler Explorer - Run compilers interactively from your web browser and interact with the assembly.
ShivyC - C compiler created in Python.
swc - Super-fast alternative for Babel.
Introduction to Compilers - Swift Playground giving an overview over the inner workings of modern compilers.
ccache - Fast compiler cache.
Starlark in Go - The Starlark configuration language, implemented in Go.