libMemcached is an open source C/C++ client library and tools for the memcached server. It has been designed to be light on memory usage, thread safe, and provide full access to server side methods.
Drizzle is a community-driven project based on the popular MySQL DBMS that is focused on MySQL’s original goals of ease-of-use, reliability, and performance.
Gearman provides a generic application framework to farm out work to other machines or processes that are better suited to do the work. It allows you to do work in parallel, to load balance processing, and to call functions between languages. It can be used in a variety of applications, from high-availability web sites to the transport of database replication events. In other words, it is the nervous system for how distributed processing communicates.