Tasque

I came across Tasque in the Foresight forums. It's no more than a front-end for Remember the Milk.
But as I'm now a big RTM user, I tried it out and it's not too bad. It additionally allows you to see all of your completed tasks and the ToDo tasks are arranged better than in RTM (in my opinion).
I'll certainly try this for the moment at least.
Another good thing about it is that it stays in the AWN dock which is nice.
I watched a video demo and it said it allows you to drag-n-drop tasks (and even Tomboy notes) to another user who you can see is online. Haven't tried this myself but sounds exciting.
Also apparently it can also be a frontend for MySQL although, again, I've no idea about this.