Bundles are like Smart Folders: they can be used to collect items into virtual piles where, unlike folders, items can be in more than one bundle at a time, and I’m pretty sure deleting a bundle does not delete the item.
Sure, but what’s the difference between that and tags?
I’m reminded of when I was digging deep into Wordpress and trying to figure out what the difference is between tags and categories. I concluded there essentially is none – some people like categories, some people like tags, and that’s that.
Basically, like folders and saved searches, bundles are lists, but tags are not. The practical implications that I can think of are:
Bundles have identifiers and URLs. Tags do not have identifiers and URLs.
Bundles can be placed within folders. Tags cannot be placed within folders.
Tags can be used to filter within a list. Bundles cannot.
Unlike folders, which can contain items, bundles, saved searches, and other folders, bundles can contain only items.
My current usage of tags and bundles might be illustrative.
I collect items across folders into bundles for particular projects. Then, to connect a bundle for a project in Keep It to the project in a task manager, I can put a link to the bundle in the note or URL field in the task manager.
I use tags to identify areas of focus (e.g., #house), document types (e.g., .receipt), etc., that I often find myself wanting to filter lists of items by.
Keep It’s really flexible. I like Notebooks, too, but it doesn’t have a good means of having the same item appear in multiple places.
I emailed the developer and got a response back within 12 hours. It’s pretty much what @mpmanti said.
Also, the proprietary .kptinfo documents are for proprietary features – something called “Smart checklists,” I think. And default file types for new files can be reset; Keep It supports native RTF, Markdown and Plain text, and can read a variety of other common file types.