I'd never heard of it until now. I'm generally a big supporter of open source software, but Archie is right, it doesn't support most of the major PLC platforms. You could probably communicate to most of them with the Modbus driver, but that isn't native support and would be missing a lot of important features (like run/stop status or diagnostics).
It doesn't even list support for OPC, which is the most common data interchange format I see these days.