If you are using memcached or are planning to you might wonder wether, giving the age of memcached being over 10 years, it is the right tool for a scalable, robust and easy to use key-value store. Below is a list of tools competing with memcached in some manner and a probably subjective rating of each.
NameDifferenceWhy [Not] Use It?
memcached%Because it simple and fast
memcachedbPersistence with BDBBecause it is a simple and fast as memcached and allows easy persistence and backup. But not maintained anymore since 2008!
BDBSimple and oldUse when you want an embedded database. Rarely used for web platforms. Has replication.
CouchDB, CouchBaseHTTP transport. Tries to find a middleground between heavy RDBMS and a key-value store cache.Sharding, replication and online rebalancing. Often found in small Hadoop setup. Easy drop-in for memcached caching in nginx.
DynamoDBHTTP transport, Amazon cloudIf you are in AWS anyway and want sharding and persistency
RedisHashes, Lists, Scanning for Keys, ReplicationGreat bindings. Good documentation. Flexible yet simple data types. Slower than memcached (read more).
RiakSharded partitioning in a commerical cloud.Key-value store as a service. Transparent scaling. Automatic sharding. Map reduce support.
SphinxSearch Engine with SQL query cachingSupports sharding and full text search. Useful for static medium data sets (e.g. web site product search)
MySQL 5.6Full RDBMS with memcached APIBecause you can run queries against the DB via memcached protocol.
There are many more key-value stores. If you wonder what else is out there look at the db-engines.com rankings.