Termcat is a markup language optimized for scientific and technical writing. It compiles to HTML and MathML.
Termcat takes inspiration from LaTeX and Markdown. From Markdown it copies the user-friendly syntax for titles, lists, links, emphasis, and so on. Termcat aims to be more powerful, however. Like LaTeX, it is a programming language and it also comes with special syntax for typographic features that are difficult to unlock using plain Markdown or HTML.
Termcat is implemented in Clojure(Script). It can be used as a command line app or embedded in a web app.
For technical details behind the implementation, please consult my blog.