What would a good GTD app need?

• Very easy input of text, photos, files, anything from many sources.
• Ability to process an item to an action.
• Ability to defer item to future date.
• Ability to process an item to a calendar entry.
• Ability to archive an item to be found easily when needed.
• Ability to easily create a project around item.
• Easy customizable categorization of actions.
• Quick access to categorized actions whenever, wherever.

And probably something else.