Recently maintained projects

C

• cmark (reference implementation, high performance executable and library)
• cmark-gfm - GitHub's fork of cmark with extensions for tables, etc.
• MD4C - very fast parser implementation with minimalistic interface (in XML-parsing analogy, it is more like a SAX parser, not DOM parser)

C#

• CommonMark.NET - available on NuGet
• Markdig - available on NuGet

Common Lisp

• cl-cmark (wraps the C library)

Crystal

• markd - written in Crystal

D

• commonmark-d (port of MD4C)
• hunt-markdown (port of commonmark-java)

Dart

• markdown - available on Pub

Elixir

• Cmark (wraps the C library)

Emacs Lisp

• cmark (port of commonmark.js)

Go

• golang-commonmark/markdown - pure Go implementation
• go-commonmark (wraps the C library)
• goldmark - pure Go implementation
• Lute - pure Go implementation

Haskell

• cmark (wraps the C library)
• commonmark-hs - pure Haskell implementation

Haxe

• necmark (wraps the C library) - neko target

Java

• commonmark-java - pure Java
• flexmark-java - pure Java, with source level AST down to single characters

JavaScript

• commonmark.js (reference implementation) - npm install commonmark
• markdown-it (high speed pluggable implementation) - npm install markdown-it
• cmark-emscripten (port of the C library to WebAssembly) - npm install cmark-emscripten
• mdx (superset of CommonMark that adds embedded JSX and import/export syntax)
• ciceromark - The CiceroMark DOM extends the CommonMark DOM for smart legal contracts; defining nodes for Clause, Variable, and ComputedVariable

Julia

• CommonMark.jl (pure Julia implementation with extensions)

Lua

• cmark-lua (wraps the C library) - luarocks install cmark
• lcmark (higher level interface around cmark, adding YAML metadata, filters, and templates)

LuaTeX

• The Markdown Package for TeX (Rewrite of lunamark Lua library for typesetting CommonMark documents in TeX)

OCaml

• Cmarkit – pure OCaml implementation

Perl

• CommonMark (wraps the C library)
• pmarkdown - pure Perl implementation

PHP

• league/commonmark - Highly-extensible PHP implementation based on commonmark.js with support for custom extensions
• cmark - PECL extension based on the original cmark implementation

Python

• markdown-it-py - A pure Python port of the JS markdown-it library; High speed and pluggable
• mistletoe - Fastest, extensible implementation in pure Python
• Marko - A pure Python implementation, focusing on easy extensibility

Ruby/RubyMotion

• CommonMarker (wraps the C library)
• motion-markdown-it - Based on the JS markdown-it library, ported to Ruby and RubyMotion

R

• commonmark (wraps the C library)

Racket

• commonmark — native Racket, with full test coverage

Rust

• comrak - Architecture based on cmark-gfm, with GitHub extensions.
• pulldown-cmark - Novel, performance-oriented architecture.
• markdown-rs - CommonMark compliant markdown parser with ASTs and extensions

Scala

• cmark-scala (wraps the C library)

Scheme

• guile-commonmark - GNU Guile Scheme

Swift

• Down (wraps reference cmark)
• SwiftMark (wraps the C library)
• MarkdownSyntax (wraps reference C library for AST access)

Tcl

• tcl-cmark - wraps cmark-gfm

TypeScript

• DefinitelyTyped (JS library bindings, NuGet)
• FlavorMark (Rewrite of commonmark.js with focus on modularizing parsing logic, npm)

Zig

• koino - Architecture based on Comrak/cmark-gfm, with GitHub extensions

Not recently maintained

These projects are based on earlier versions of CommonMark and are now obsolete. But they might be good starting points for new work.

Dart

• mdown

Idris

• idris-commonmark

Haxe

• comark

Lua

• luacmark
• commonmark-lua - luajit + FFI

Python

• pycommonmark
• commonmark.py - deprecated in favor of markdown-it-py

Swift

• CommonMark.swift
• SmarkDown.swft - Pure Swift