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.
sccache - Shared Compilation Cache.
tal - Implementation of Typed Assembly Language (Morrisett, Walker, Crary, Glew).
microml - Minimal ML, type-inferred, compiled, and/or interpreted in less than 800 lines.
libffi - Portable foreign-function interface library.
go2ll - Toy go compiler to LLVM.
libFirm - Graph based intermediate representation and backend for optimising compilers.
mimalloc - Compact general purpose allocator with excellent performance.
BOLT - Binary Optimization and Layout Tool - A linux command-line utility used for optimizing performance of binaries.
Intel(r) SPMD Program Compiler - Compiler for a variant of the C programming language, with extensions for single program, multiple data programming.
hobbes - Language and an embedded JIT compiler.
Functional Language Research Compiler (FLRC) - Designed to be a general compiler framework for functional languages.
dino - Compiler / PL Experimentation in Rust.
MazuCC - Minimalist C compiler with x86_64 code generation.
Clang Build Analyzer - Can be useful to figure out what takes time during compilation of one source file.