I'm displaying both Sets (which contain Cards) and Folders (which contain Sets) on the same page. Ideally they'll both be tiles. I'm not sure how to make it easy for the user to tell the difference though, other than putting "SET" or "FOLDER" in the corner of the tile, which doesn't feel right.
Here's what I'm working with:

Note that both of these can be either a Set or Folder, this is a work in progress. Any tips/opinions would be awesome!
Edit: This is for a personal study tool - flashcards are grouped into sets, and when I have a bunch of sets that can be grouped, I'll put them in a Folder. I think this can help with "overall" studying too - like this:
> Folder "Thai"
>> Folder "Thai Level One"
>>> Set "Thai Sentence Structure"
>>> Set "Thai Basic Vocabulary"
>> Folder "Thai Level Two"
>> Set "General Thai Review"


