Varnish is a modern application level reverse proxy for web sites & services written with performance in mind. Varnish incorporates some advanced features to stretch the kernel as far as possible. Wikia relies heavily on varnish to serve a peak traffic of close to a gigabit/sec out of 3 different datacenters. Each one with two Varnishes working as a pair serving thousands of requests a second.
Chris will talk about CouchDB's offline replication, their robust storage system, using incremental Map Reduce for consistent live access to schemaless data, portable applications, and a short list of current