PEM is a PHP/MySql script under GNU license that allows registered users to provide everybody with extensions pertaining to various categories.
To find the extension you're looking for, you can either:
To make the search easier, 3 filtering criterias are available
Use keywords to find the desired extension
Having found the desired extension, be sure to check it is compatible with the version you're currently using before downloading.
To contribute, you only need an account with the extensions manager
If there is a FluxBB forum on the website, and you are registered with it, you can login with your forum user and password.
Just click on Register and fill in the required information.