How this is supposed to be used

Say we want to start a reddit-like forum about cats:

We git clone this project.
Give it a unique id that will serve as the id of the shared folder.
Write the rules script that will validate each cat before it's posted.
Compile everything into an Android or iOS app.
Publish the app and let users download it.
Each app instance uses the folder id to find other users of the forum.

In this diagram:

All the nodes are IPFS nodes.
Square green nodes participate in the same forum.
Solid lines are IPFS connections between nodes.
Dotted lines are additional IPFS connections discovered by the forum nodes.

This means that when a1 wants to add a new file in the forum, it sends its hash to c1, c3 and b4 and they later send it to d2.

The rules script can be arbitrarily complex:

It may just check that a new post contains a description of length 200-500 words.
It may check that the description has a valid URL to a cat picture.
It may actually download that URL, check the size of the downloaded picture and its format.
It may even run an ML model to verify that the picture contains a cat and not something else.
It may contact a captcha service and sign the post with a RSA key if the user answered the captcha correctly.