iA Writer - Minimal Design, Maximum Focus
Woolah - Knockout Photo challenges with your friends.
MacDown - MacDown is an open source Markdown editor for OS X, released under the MIT License.
SPAR! - Challenge your friends. Put money on the line. Get better.
MWeb - Pro Markdown writing, note taking and static blog generator
ShutterSpots - Find & share photo locations nearby & all over the world!