As part of the MacHeist bundle there was a program called TaskPaper. After looking into it I found it pretty limited. As did Henrik Nyh:
I came across TaskPaper the other day – a simplistic to-do list app currently in development by Jesse Grosjean, who made the equally simplistic text editor WriteRoom.
– — However, I edit my text files in TextMate. Using something else for to-do list text files complicates things. So I made a TextMate bundle for it