Part Taskpaper — part Markdown editor. The long awaited app from Hog Bay Software, FoldingText, is now in the Mac App Store.
For their launch, they have reduced the price 40%. If you've kept up with the release notes written by the developer, Jesse Grosjean, then you will know that he had originally planned on releasing this app with a fairly substantial price tag.
After using this app in its beta stages, the capabilities of this Markdown editor/To-do list is amazing and fully worth the price tag he has attached to it.