The Couchbase Server is completely compatible with the memcached protocol, which is a widely adopted protocol for storing information in high-performance, in-memory caches. This means than any existing memcached client libraries and applications using these libraries can be migrated to with Couchbase Server with little or no modification.
There are numerous challenges faced by developers who currently use memcached with a traditional RDBMS which are resolved by a move to Couchbase Server. For instance, if you currently use a memcached layer for data service and a traditional RDBMS, your database could become overloaded and non-responsive when memcached nodes go down. With a Couchbase Server cluster, your information will be automatically replicated across the cluster, which provides a high availability of data, even during node failure.
For more information about Couchbase Server as a replacement for memcached and RDBMS systems, see Replacing a Memcached Tier with a Couchbase Cluster and Couchbase Server Manual 2.0, Couchbase APIs.