What do you use for a todo list software / service? Not project management, just a todo list, but one that is full-featured. Specifically I want something that can:

1. Create hierarchical lists, so tasks with sub and subsub tasks.

2. Overlapping tags / categories for tasks.

3. Triggers for activating tasks. Simplest would be time-based. So a task would only show up on the todo list at a certain date, and perhaps only stay there for a date range. I also need tasks that are triggered based on other tasks. So task B only becomes active (i.e. shows up on the todo list) when task A is completed. Composite trigger rules with multiple conditions would be ideal.

4. A way to view only a subset of tasks, perhaps randomly chosen. So something like "task of the day", which would be randomly picked from a pool of tasks. Ideally one can have multiple pools, etc.

Anything like this exists? Anyone care to make it? ;-)