How to recreate PirateBox’s functionality?

What is the easiest way to recreated some of PirateBox’s functionality on most routers that can use OpenWrt?

What I want to do:
stick a USB drive in a router, people can connect to that router and will be directed to a page that tells the point of connecting to this non internet connected router.
Users can download files and hopefully upload as well.
There would also be a very basic chat screen where everyone could chat.

Piratebox also had a message board/image board. While this would be nice, it adds to the complexity and seemed to be the part that crashed the most on PirateBox.

I did a search before posting but could not find similar post.

I looked on the main page and found:

Would this enable some kind group lan type chat?

Yes very noob questions.