Practice on the PHP Engine

Implement a bulletin board. The user visits the site, selects a category, and places their advertisement in it.

Implement a forum with mandatory registration. A registered user can create topics and reply to them. In addition to regular users, there should also be moderators who can delete any topics and ban users, as well as a site administrator who has access to the admin panel.

Implement a social network. How it will work: a user registers, fills out their profile, and then can add friends, communicate via private messages, leave messages on their own and others' walls.