memcached is described as 'Free & open source, high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load'. There are more than 10 alternatives to memcached for a variety of platforms, including Linux, Windows, Mac, Online / Web-based and Self-Hosted solutions. The best alternative is Redis, which is both free and Open Source. Other great apps like memcached are Varnish (Free, Open Source), Cloudify (Free, Open Source), Hazelcast (Free, Open Source) and GridGain In-Memory Data Fabric (Paid).
yrmcds is a memory object caching system with master/slave replication. Currently, yrmcds supports two protocols: the first is an enhanced memcached, and another is a protocol to implement distributed resource counters.