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 is somewhat like Memcached, but persistent.
Redis is implemented in C with a test suite written in Tcl. The test suite includes a Tcl client library.
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: