Redis is an in-memory data structure store that persists on disk. The data model is key-value, but many different kinds of values are supported: Strings, Lists, Sets, Sorted Sets, Hashes.
It has a Tcl client interface. It is somewhat like memcache, but persistent.
Retcl is an event-driven, object-oriented, Redis client library targeting the Tcl scripting language.
Things that Retcl does which are missing in Salvatore's client are: