Here is the list of PHP classes I contributed to the community so far. I published most of these classes to phpclasses.org, so only notable classes are listed here. Use the contact form if you need to submit any query about these classes.

Reference Collection
This is a simple class helps you to manage the references of php variables. I wrote this class when I tried to re-invent PHP serialization. This class will be useful when you travel through properties of an object or values of an array and you don't want to loop forever when there is a circular reference. This class is nominated to December 2010 Innovation Award (rank 6).

Magic Array
This class can provide enhanced functionality over traditional arrays. It extends the ArrayObject class to allow treating the class object as arrays. The class provides functionality like allowing array keys to be case insensitive and can remove array entries by entry value. This class is nominated to February 2008 Innovation Award (rank 4).

HTTP Upload
This class can be used to handle files that are uploaded to a server via Web forms. It supports applying upload filters to restrict the files that are accepted according to configurable criteria like: file name extension, MIME type, file size, width and height in case the files are images. It also supports handling uploads of multiple files. It can also add prefixes to the uploaded file names, giving unique names or changing the file name extension for security reasons.

HTTP Download
This is a very old class, I firstly wrote it for my file manager project. It can handle HTTP requests that ask to resume the download of files that were partially downloaded previously. So, it supports any download manager program that the users may employ. It can also handle user download abort requests so the download process stops immediately. Later I see this class is used in older versions of  RapidLeech, and it's also used in PHP-Fusion project.

SecureURL
The class uses encoder to encrypt URL parameters. It uses PHP output buffer capture support to automatically process the URLs of the links and forms of the current page. An optional filter may be specified to restrict the URLs that are altered by the class. When the current page using the class is loaded, it decrypts the parameter variables and updates the respective global variables.