re2c. “re2c is a lexer generator for C/C++”. See skvadrik/re2c on Github. This might be fast enough that I would use it instead of writing a hand-written scanner.
cmark. “CommonMark parsing and rendering library and program in C”. Also see Github’s fork at github/cmark.
GitHub Flavored Markdown Spec
Text Editor Performance Comparison
bcachefs. “The COW filesystem for Linux that won’t eat your data”
4 APPROACHES TO NATURAL LANGUAGE PROCESSING & UNDERSTANDING