What are the differences, advantages, dis-advantages between Riak and CouchDB? I haven't found a comprehensive comparison till date. Edit: Yes, I have been a bit lazy not to go and try Riak first hand. I think I will do it sooner then later but as of now, any light on the subject will be appreciated.
They serve different purposes. Riak is a DHT (for key sharding) layer intended to run on top of different backends, just like Dynamo. CouchDB has an integrated storage engine. Riak doesn't support range queries (nature of DHT). I'm pretty sure CouchDB does, which is easy for a single node. CouchDB doesn't scale in the sense that it doesn't do any automatic sharding yet. It's quite possible to use CouchDB as a backend…
The Scalaris DHT supports range queries, I think.