I wrote a KV store on top of Bit.ly once: https://github.com/apg/bitdb -- The "todo list" example has a good description of what's going on: https://github.com/apg/bitdb/blob/master/examples/todo.py

And I know of a generic blob store on top of (older) Snapchat API: https://github.com/hausdorff/snapchat-fs

It's really fun to "exploit" APIs in this way to create alternative uses.