PQClean
Clean, portable, tested C implementations of the schemes in the NIST post-quantum project, used as a source by other libraries.
Why this is listed
Its stated objective is the standalone C implementations themselves, released under CC0 with per implementation licence files, and other projects vendor them directly, so the implementation is the product.
PQClean describes itself as an effort to collect clean implementations of the post-quantum schemes in the NIST post-quantum project. Its stated objective is standalone C implementations that are heavily tested and useful to other projects.
That last part is the reason it matters beyond its own repository: the Open Quantum Safe project integrates PQClean implementations into liboqs, which then exposes them through C++, C# and Python wrappers and through forks of OpenSSL and OpenSSH. A defect in a widely reused reference implementation travels a long way.
The repository is retired. Its README opens with a retirement notice stating that PQClean is archived as read-only, and points readers to the PQ Code Package organisation for maintained implementations of the standardised algorithms. On licensing it states that each implementation subdirectory carries its own LICENSE file, that files in its common directory are public domain or MIT, and that all other code in the repository is released under CC0. It is still listed here because it remains readable and is vendored into other projects, but anyone taking code from it now should know that it is not maintained.
Sources
Checked against these sources on Sep 4, 2026. Listing is not endorsement, and nothing here is ranked or scored.