What are some alternatives?
When comparing Assemble and Metalsmith, you can also consider the following products
GatsbyJS - Blazing-fast static site generator for React
Wintersmith - Flexible, minimalistic, multi-platform static site generator built on top of node.js
Nanoc - A static-site generator written in Ruby
Hexo - A fast, simple & powerful blog framework, powered by Node.js
Nikola - Nikola is s static site generator tool written in Python.
Jekyll - Jekyll is a simple, blog aware, static site generator.