I found it useful to stick to paper while I was learning the system. After you start to get comfortable, you'll make some minor adjustments and paper is unbeatable for allowing rapid changes. If you code something up or tie yourself to a software tool too early, you'll end up a little more stuck with how it works rather than what's best for your particular situation.
(and once I was comfortable, I of course coded up my own little web based system which was basically just a little web app with infinitely nestable lists, a nice AJAX interface for expanding, collapsing, adding sub-items, and a nightly cronjob to move items from the tickler lists to the INBOX list).
Tools for email would be really nice, though, since you definitely can't do that on paper. And much of what he talks about seems very applicable to email, but I'm not sure how to actually do them in an email client. Email is like a microcosm of the entire GTD system.# Ian Bicking
Todo.sh (bash script to manage a text file) is quite nice. See screencast here - http://www.todotxt.com/library/todo.sh/
I have to agree with this comment. I've been using todo.sh as well and it works wonderfully. It's easily parsed, there is a community working on making it better. And there is even an initial port to Python as well.
I'm using a similar command line tool for managing my todo items: http://swapoff.org/DevTodo# Jan-Wijbrand Kolman