Sharedance - Centralizing data and PHP sessions
"Sharedance is a high-performance server that centralize ephemeral key/data pairs on remote hosts, without the overhead and the complexity of an SQL database.
It was mainly designed to share caches and sessions between a pool of web servers. Access to a Sharedance server is trivial through a simple PHP API and it is compatible with the expectations of PHP 4 and PHP 5 session handlers."