Offline Markdown editor with Git client?

I've been trying to find a good offline Markdown editor with the following features:

Must have:

  * Instant preview, either inline or side-by-side.
  * Git client, allowing saving directly to a remote repo
  * Self-standing, i.e. not a plug-in for an editor or IDE.

Nice to have:

  * Cross platform, ideally for all thre OSs; MacOS is minimum.

Any recommendations?