Key-value databases are catching fire these days. Memcached, Redis, Cassandra, Keyspace, Tokyo Tyrant, and a handful of others are surging in popularity, judging by the contents of my feed reader.

I find a number of things interesting about these tools.

• There are many more of them than open-source traditional relational databases. (edit: I mean that there are many options that all seem similar to each other, instead of 3 or 4 standing out as the giants.)
• It seems that a lot of people are simultaneously inventing solutions to their problems in private without being aware of each other, then open-sourcing the results. That points to a sudden sea change in architectures. Tipping points tend to be abrupt, which would explain isolated redundant development.
• Many of the products are feature-rich with things programmers need: diverse language bindings, APIs, embeddability, and the ability to speak familiar …