classh is yet another wrapper around ssh for running commands on a number of hosts concurrently. It is similar to xCAT, pssh, Cluster ssh, and a gaggle of other utilities. The only pre-requisite for classh is Python 2.4 or later, and no formal installation is required; a copy of the classh.py file is sufficient to run commands. The SSHJobMan class from classh can be used to create custom job management scripts. This class lets you either wait until all output has returned from a batch job or process the results as they become available by incrementally polling the running job. The output, error messages, exit code, and start and completion times of each job are stored in the results. It's been tested on jobs of over 25,000 hosts and handles over 10,000 hosts per hour across a WAN and without noticeable impact on the administrator's host.
Galera wsrep provider is a dlopenable generic replication library which implements the wsrep provider API. It provides very efficient synchronous replication, and multi-master and "parallel applying" capabilities for opaque data buffers. Its primary focus is data consistency. A transaction is either applied on every node, or not at all. It works anywhere TCP works, including on WAN, and can utilize UDP multicast where available. It is used by the MySQL-wsrep patch project to create true multi-master MySQL/InnoDB clusters.