The initial idea on how to do serialization was contributed by KH Wild to the php3 mailing list. It was limited to serializing arrays of at most three dimensions, though. We worked on his solution, improving it to arrays of arbitrary depth and later rewrote the function from scratch, turning it upside down. Our new serialization code can now handle any first order data type available to PHP and is easily extensible. It is also encapsulated in a class, keeping the namespace clean. While we were at it, we made session cookies more secure by not using uniquid() directly, but a md5() hash of uniqid().
Cameron Taggart and Guarneri Carmelo contributed ODBC support. Szandor van Verseveld contributed Postgres support. Scott McMullan contributed some nice ideas for cleanup and is working on Sybase support.
A lot of people provided helpful hints and occasionally patches. Please see the file CREDITS for a complete list of contributors, testers and inspirations.