Days Ago is a Chrome Application (a new style 'packaged app') which you can install in Chrome and launch from the browser. It lets you type in very simple "todos", for instance:
Write letter to the bank in 3 days
This will appear as a task Write letter to bank with a due date of 3 days. Tasks can then be coloured according to their due dates, and removed when completed.
Days Ago is currently available in the Apps section if you are on the Chrome Developer channel, or it can be installed by visiting https://chrome.google.com/webstore/detail/jgpkfclnhphhkocokeikoiabmjeejdlf.