[RocksDB](https://rocksdb.org/) isn’t a distributed storage system, fwiw. It’s an embedded KV engine similar to LevelDB, LMDB, or really sqlite (though that’s full SQL, not just KV)
To be perhaps overly detailed: Hbase is an open source approximation of bigtable. Bigtable _uses_ leveldb as its per-shard local storage mechanism; Rocks is a clone+extension of leveldb.
Bigtable and hbase are higher level and provide functionality across shards and machines. Level and rocks are building blocks that provide a log-structured merge tree storage and retrieval mechanism.