Lambdo is a To Do List manager written in Haskell. I have not implemented an interface yet. Yeah, that's sort of major, but I think the underlying backend is more difficult, especially since Show is properly instantiated for my ToDo type. The coolest part of this thing is "calculatePriority" which does exactly that. ToDoLists are ordered using a heuristic (which still needs a bit of tweaking) that takes into account the time between the current day and the due date, the assigned category, the status (i.e. in progress, open), and the user-assessed importance. As I said, the weighting may need some tweaking, but it's still pretty cool.