Take a look at Basho's Riak. It has a number of things in common with CouchDB: Erlang-based, Javascript MapReduce API, HTTP transport, JSON document format and multi-master replication. It doesn't aim to be quite as simple as CouchDB (CouchDB is more "opinionated"), but they give you a lot of options for adjusting CAP parameters to meet the needs of your application, per-write.