Hi There!

I have spent a good part of the last couple of months looking around for a decent task management package. Features I am looking for are:

Cross Platform - Windows 32/64 bit client, Web, Android (Native App)

True Multi User 
 - Ability to assign others tasks, or groups of tasks
 - Ability to be notified when a task or subtask is complete
 - Indicators for Progress
 - Nice easy way to see others tasks 

Ability to Import and Export Tasks or Task Templates
Categories
Multiple Task Lists (Home, Work etc), plus Sublists (Home Might contain lists for grocery, repairs, holiday)

Simple clean fast interface. Very quick to create tasks and navigate around the application

Actively developed. Good Documentation, preferably an on-line community for discussion.

Not too expensive. $50 per year per user would be the most we really want to pay, but would stretch a little for something fantastic.

Anyone able to recommend something?