Alex King has created quite possibly the most install-intensive To Do list application ever: tasks.

Written in PHP and Javascript, tasks requires you to be running Apache, PHP and MySQL before you can even begin to jot down the things you'd like to do. That said: it's excellent! Extremely well-written, sporting an elegant UI, fast and responsive (by using DHTML where appropriate), tasks has become, in just two days, my favourite To Do list application. (And the part of me that also likes perl likes tasks a bit because of it's extreme geektastic barrier to entry :-)) If you happen to have the above-mentioned installed and you're looking for a task manager, check out tasks. Discuss

(As an aside: I'm also writing this post via Mozilla Firebird which is working ridiculously well under OS X).