This is a PHP script to register and log users in a website, and shows the Online users. It's created with the method based on classes and objects (OOP). It uses PHP, MySQL and Ajax / JavaScript (but also it works with browsers which has no activated JavaScript). The connectiong to MySQL is made with MySQLi.

Features of Register Login User Online:
- Not allow two accounts with the same name or e-mail.
- Allow only one account with the same IP, or registered from the same browser.
- Not allow two visitors to log in with the same name (on different browsers). If there are two logged users with the same name, the first will be logged out and will alert a message that he/she can re-log in.
- Each user has a "rank" stored in database (a number). Then, the value of this rank is sored in Session and can be used to display content in the website according to the user's rank.
- The e-mail address, and the minimum and maximum number of characters added in form fields are validated both on the client side (with JavaScript) and server-side (with PHP).
- It allows up to 4 failed login attempts (incorrect password or username), then the visitor can try a new authentication after 10 minutes. This is a protection against bots.