http://wasitup.com uses Tokyo Tyrant, but I'm nearly finished with a rewrite to Redis. Tyrant was abandoned because of a nearly non-existent community, poor documentation, and some replication issues.
Redis was selected over MongoDB and Cassandra since it scales down, is lightweight (with virtual memory enabled memory is not an issue anymore), and extremely easy to install and manage.
Redis was selected over MongoDB and Cassandra since it scales down, is lightweight (with virtual memory enabled memory is not an issue anymore), and extremely easy to install and manage.