Mango is most commonly used as you discribe connect to PLC's and controllers. Mango can produce a browser based HMI for you or Mango can also be a Modbus TCP slave to another HMI.

To connect Mango to a PLC it just needs to support one of the protocols Mango includes. Modbus would be the most common but there is also an Allen Bradley Ethernet IP and PPPC driver.

See here for some getting started help documents: http://help.infiniteautomation.com/