So, if Tokyo Cabinet got Kyoto Cabinet as a successor, Tokyo Tyrant got Kyoto Tycoon as its successor. But this time it is not only an implementation language port, as Kyoto Tycoon also behaves as a cache system with support for auto expiration (something similar to memcached). Moreover Kyoto Tycoon is offering a RESTful-style interface.
You can read more about Kyoto Tycoon ☞ here.
Update: Brenden Grace has ☞ a post to which Mikio Hirabayashi, Tokyo and Kyoto creator, responded.