DoStuff is a unusual application - it's simple, and it is based off of a "standard".
For those of you who don't know, there is a project called todo.txt, which plans to "Future proof" your todo list by storing it in a file called... todo.txt of all things!
A product of the Ubuntu App Showdown, DoStuff is simple.
While I personally won't use DoStuff because of what I do (I need something a little more complicated than todo.txt can provide), I highly recommend using DoStuff, if todo.txt is your thing.
You can install it via PPA, at least until it lands in the Ubuntu Software Center. Instructions are at the link. For more on the dangers of PPAs, please look at this Ask Ubuntu question.
Download the official 2buntu app for both Android and Ubuntu Touch.