I like that Memcached allows for storage in RAM. It is Key-Value, but storing a JSON string is easy and quick. Especially so when using for it's intended purpose as a cache without worrying about persistence. It's written in C, very close to the metal. Additionally, development on it is very active - with the most recent stable release a few months ago. I especially love that it can distribute its hash table across multiple machines, thus improving speed and reducing overall workload. Review collected by and hosted on G2.com.