ManDrake is a native, open-source man page editor for Mac OS X. It has syntax highlighting,
mdoc syntax validation and a live-updating rendered preview.
Long story short, I was sick of writing man pages in an endless cycle of edit-view, edit-view so I decided to do something about it and made this editor. It's a bit rough around the edges, but it works really well for me.
The latest version of ManDrake requires OS X 10.7 or later, and is built as an Intel 64-bit binary.
The ManDrake source code is distributed under a BSD license and is available on GitHub