hugo (Apache 2.0)
zola (MIT) : A fast static site generator in a single binary with everything built-in.
Publii (GPL 3.0) : Publii is a desktop-based CMS for Windows, Mac and Linux that makes creating static websites fast and hassle-free, even for beginners.
Susty (GPL 2.0) : A tiny WordPress theme focused on being as sustainable as possible. Just 6 KB of data transfer.
Grav : PHP