Any suggestions on having master-master replications around the world by nosql solutions?
The two NoSQL DBs that come to mind when mentioning cross datacenter replication ("master-master replications around the world") are:


Cassandra
Couchbase


Both of them seem to have fairly decent cross datacenter replication abilities, so which you should go with should be decided upon in a different manner.

If you want a KV-Store (where you can simply look up binary blobs using keys), then you ought to go with Couchbase.

If you want something similar to the SQL concept of rows and tables and whatnot (albeit, without relational functionality such as JOIN), then Cassandra and CQL might suit you better.