ability to add custom lists to items

I believe it would be handy to be able to add custom lists to each item.  An example is being able to add a list to a Trello card. I guess this would need to be a new field type.  The use would be many and varied but a simple example is that it could be a list of sub tasks within an item that need to be complete.  The list would make them more of a prompt than an assigned Podio tasks.  Also if it were a field you would be able to have the list appear somewhere more useful in the item than in where tasks sit.