What are some alternatives?
When comparing Wintersmith and GatsbyJS, you can also consider the following products
Metalsmith - An extremely simple, pluggable static site generator.
Jekyll - Jekyll is a simple, blog aware, static site generator.
Nikola - Nikola is s static site generator tool written in Python.
Hexo - A fast, simple & powerful blog framework, powered by Node.js
Assemble - The static site generator for Node.js, Grunt.js and Yeoman
Hugo - Hugo is a general-purpose website framework for generating static web pages.