By Pavlo Baron and Kresten Krab Thorup:
In the first step, it will allow Mongo drivers to seamlessly connect to it using Mongo Wire Protocol and to map to the underlying Riak data store. This can help migrate the data store of existing MongoDB based applications to Riak.
In the next step it also might be interesting to have a Mongo based Riak backend.
No need for the second step.
Original title and link: Riak_mongo Makes Riak Look Like Mongo to Clients ( ©myNoSQL)