MongoDB ObjectID's are designed with similar goal in mind - time based, distributed, uncoordinated, "probably" unique: http://docs.mongodb.org/manual/reference/

MongoDB ObjectID's are designed with similar goal in mind - time based, distributed, uncoordinated, "probably" unique: http://docs.mongodb.org/manual/reference/object-id/ http://docs.mongodb.org/manual/reference/object-id/ I say "probably" unique because they depend on the 'machine identifier' being unique, which the ruby driver implements by grabbing the first 3 bytes of the hostname's md5 hash.