Wyam is described as 'simple to use, highly modular, and extremely configurable static content generator that can be used to generate web sites, produce documentation, create ebooks, and much more'. There are three alternatives to Wyam for a variety of platforms, including Self-Hosted solutions, Windows, Linux, Mac and Python. The best alternative is Jekyll, which is both free and Open Source. Other great apps like Wyam are MkDocs (Free, Open Source) and Bridgetown (Free, Open Source).
Jekyll is a simple, blog aware, static site generator. It takes a template directory (representing the raw form of a website), runs it through and Liquid converters, and spits out a complete, static website suitable for serving with Apache or your favorite web server.
MkDocs is a fast, simple and downright gorgeous static site generator that's geared towards building project documentation. Documentation source files are written in Markdown, and configured with a single YAML configuration file.