After having tried many of the free & paid solutions here over the years, I've created my own open source solution in pure T-SQL that outputs documentation in Github Flavor Markdown, sp_doc
as part of a larger suite of free scripts called Express SQLDBA MultiTool.
ThisDoing it via T-SQL reduces the complexity of relying on a third party application, PowerShell module/library, etc. and leverages the built-in power of Extended Properties to make the database self describing. It can be easily hooked into automated deployment workflows to produce an always up-to-date view of the database.
Databases can be complex, disastrous things. Not every database admin, developer, or analyst has the time to learn the ins and outs of a database in order to just do their work. To make things worse, few products and fewer free options exist to help present databases in a human readable format.
sp_doc
's goal is to generate on the fly database documentation in Github Flavor Markdown (GFM). This means you now have a free and extensible self-documenting database!
Update: It can now also be installed via dbatools' Install-DbaMultiTool command as well.