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Alternatives: asciidoc.

Maps easily to docbook, and has a heap of extra features.

And it's also relatively close to markdown (biggest change is links).

The asciidoctor project also has browser extensions for rendering which are really nice. For the lazy: http://asciidoctor.org/

Github can render asciidoc. Do they use asciidoctor.JS?

I found the lib was rather big :/

This. All the benefits of markdown (and similar), with a decent toolchain, version control capabilities and exporting to various formats.