Features for a checklist site

Items can be easily reordered (drag and drop like Nozbe)

Checklist can have mutiple tags

Checklists items can be nested

Checklists themselves can be nested (supports hierarchical links or sub level checklists)

Non-checklist items can be added (if you had a checklist for houses, you could copy the checklist and fill in the street address to separate copies of the same checklist)

Ability to group checklists

Ability to lockdown a template checklist

Ability to query across checklists in a group (in a checklist for houses, show me all the ones where "Swimming pool" is checked)

Multiple dates can be associated with a checklist item

Dates associated with the checklist or checklist items can have tags

Checklist items can have tags

Checklist items can be imported and exported in a mindmap (freemind) format

Checklists are stored in XML

Checklists are compatible with phone browser (WAP)

Ability to assign checklist items to others to verify completion

Ability to assign completion time to a checklist item