I like a simple site which allows users to create a list and be able to drag and drop to change order of items. And save results as file as well as in a URL.
-Drag and drop ability for ordering
-Create single or as many lists as they would like (each list is in a new tab)
-Account optional (user can login if they want more privacy or else they can be anonymous)
-Lists can be access via a URL (think of [url removed, login to view] where you upload an image and have URL to access this image. Same thing... so if anonymous, then URL goes directly to list. If account, then go to login page). URL should be randomly generated and have minimum of 10 random characters. System should not generate same number twice.
-Anonymous lists should be automatically deleted after 90 days
-If user wants Account, it is simply email address and password (with remember me function to save info in cookie and bypass login entirely)
-List is simply text with limit of 4000 characters per line
-Option to have numbering next to list (using <LI> tag perhaps to do automatic numbering?)
-Lists should have 1 column by default (title). But user can add additional fields by clicking ADD NEW FIELD. And remove fields by clicking DELETE FIELD button next to FIELD.
-should use MySQL and PHP
-Speed is very important
-Dont worry about visuals.. I could do visuals
-Must use AJAX for adding items/fields to the list so no refresh
-After add/edit/drag and drop, user can click SAVE LIST to save changes
-User can add more than 1 list (no limit)
Users should be able to embed lists on other sites such as MySpace or blogs.