I recently started some documentation work for a project written in C#, and after researching tooling for auto-generating docs from the code base and falling down a rabbit hole, I emerged from the other side and found DocFX. Microsoft owns the project, but I think they rescued it from an abandoned project at some point. While it has a lot of features well suited to C# code bases, I also unearthed a plethora of other fantastic documentation features to suit projects written in any language.
DocFX Flavored Markdown (DFM)
Bringing yet another flavor to the sometimes too simple Markdown, DFM includes all GitHub Flavored Markdown syntax and adds a lot of syntaxes specific to using DocFX to build your documentation. Some of the syntax is so useful and pleasant to use, I hope other platforms adopt it. This isn’t a comprehensive list, but here’s what I’ve found most helpful so far. You can find a full list on their website, but not all in one place.