[Glastonbury] Recommendations for to-do list apps?

[Ian Dickinson]

Anyone have any recommendations for a decent to-do/task list manager
for Linux? I was using Green Parrot's ActionOutline on windows, but
now that I've switched my development environment entirely over to
Linux I'd like something better than nedit :-)   The main feature I
use is hierarchical classification of project/task/todo items;
would-be-nice features are xml output, deadline tracking,
mutliple-category classification, task priorities and drag'n'drop
re-arrangement.

I've been hearing various rumours of good or excellent to-do managers
for the Mac ... is there a response from the penguinistas yet?

Ian