Bandrew

• Wiki-like version history
• Documents stored in a subversion repository
• Integrated GUI subversion browser
• Subversion can be pointed to a local drive, a remote server, or a host offered by the manufacturer
• GUI history browser with diff highlighting and history search
• Documents are saved in markdown.
• Documents editing in both markdown and a rich text environment
• Typing a markdown syntax (e.g. ###) in the rich text environment will automatically convert the line to that style (e.g. h3)
• TextMate’s keyboard shortcuts

I guess TextMate comes pretty close, but I like to edit in rich text.