can they be used to do similar things? yes. are there overlapping use cases? indeed. Are they going to overlap more and more as time goes by and they try to exp

can they be used to do similar things? yes. are there overlapping use cases? indeed. Are they going to overlap more and more as time goes by and they try to expand out of their niches? absolutely. But they fall squarely in different categories: Riak KV, MongoDB document (and HBase Column, Neo4J Graph for example)