Markdown Clips is a collection of Basic and Extended Markdown syntax snippets, for use in Panic Inc's Nova.
Markdown Clips uses triggers to assist with autocomplete. Unlike some other markup languages, the triggers are only part of the words so they don't interrupt your writing.
There is keyboard shortcut support for some of the formatting options. (e.g. Cmd+B for bold and Cmd+I for italic).
You can also open the Clips sidebar and visually browse the library. Nova will let you double click, or click and drag into the editor.↷ Get it on GitHub