1. MySQL Sandbox http://mysqlsandbox.net Free software (GPL)
One (unix) host
Many database servers
Single or multiple sandboxes
Customized scripts to use the servers
Standard or circular replication
Installs IN SECONDS
Installs to remote servers (experimental with Gearman)
MySQL Sandbox is a tool that installs an additional MySQL server in a few seconds.
You can have more than one database servers in your host, all of them independent from each other. Installing a new server with MySQL Sandbox is a matter of seconds. You can install either a single sandbox or a system including multiple ones. Sandboxed servers can be stand-alone or related in standard or circular replication systems.
It is free software, and it works on most every unix OS. In combination with Gearman, it can install and setup replication systems across multiple hosts.