GatsbyJS - Blazing-fast static site generator for React
Metalsmith - An extremely simple, pluggable static site generator.
MiddleMan - A static site generator using all the shortcuts and tools in modern web development
Nikola - Nikola is s static site generator tool written in Python.
JBake - "Jekyll of the JVM"
Octopress - A static blogging framework for hackers, based on Jekyll