Nitro is a very promising new todo list app for the Mac (plus a bunch of hippie platforms). It keeps your notes in a plain text file on Dropbox, and is available free from the Mac App Store.
Nitro works around a todo.txt file, the favorite todo list format of nerds everywhere. And as it exists on Dropbox (or Ubuntu’s cloud service, for the beardos amongst you), you can open and monkey with this file using any app you like.
Or rather, you can read from it. In my testing Nitro refused to accept changes made from other apps. Even quitting Nitro, then editing the file, then relaunching Nitro wouldn’t get it to see the changes. In fact, you can delete the contents of the file — or even the file itself — and it will be recreated on next sync.
What you can do is use the web app, which is identical to the OS X app.
Nitro uses the familiar sidebar-and-content layout, with a list of lists on the left, and a few “Focus” views above that. These let you focus in on tasks due today, or up next, or all tasks. Checking off a task makes it disappear from everything but the All Tasks view, and from there you can archive it.
Adding new tasks is easy, and you can type in your own tags, add a due date (with a very nice date picker), and create your own lists to further organize things.
As I said, it shows a lot of promise. Currently I’m using Gmail, IFTTT and Gmail filters to roll my own task manager, and it’s working great (it even integrates with the iOS Mailbox app). But I will certainly be watching Nitro, even if it is open source.