What software does plc use?

Programmable Logic Controllers use "proprietary" software generically called "ladder logic" which is a special form of programming that takes logical inputs and using internal timers and relays it creates controllable circuitry which becomes the outputs. It is a modern replacement for relays, and relay logic. For example Allen Bradley uses their own software that is written specifically for their PLC's. A really good PLC is from Automation Direct which makes a very affordable PLC with cheap or free software. You can find used PLC's on eBay, and there are all kinds of training classes on the Internet. Hope this info helps. Good luck!