Ratis replicated map is an implementation of a sorted map (think TreeMap) as a replicated state machine. This is not under examples because it is intended to be used in production where a simple in-memory map is sufficient to hold the data. The data is fully cached in memory, but it is still durable since raft log is used as a replicated log, and data is snapshotted periodically.
The replicated map (RMap) is not only the state machine implementation, but all of the remaining code, including the client and querying capabilities which is built on top of the other modules. In that sense, it is dog-fooding the ratis library to implement an end-to-end solution for a replicated in-memory data store.
Replicated maps are conceptually similar to ZooKeeper/Etcd/LogCabin where the data is hosted in a known cluster configuration and is not sharded. All the servers in the cluster participate in a single RAFT ring.
The data model is that users can create independent RMap instances in the cluster and read / write or scan the data as key value pairs in those replicated maps. A replicated map named the meta map contains information about all of the other maps in the cluster.