“Piston” is the name for an automation routine created in webCoRE or CoRE, which are community developed rules engine smartapps for SmartThings. The native SmartThings automations work for some people, but are generally pretty limited in what they can do. webCoRE and CoRE on the other hand are capable of extremely complex rules, and can be used to create pretty much any automation you can imagine. It’s well worth looking into IMO.
[FAQ: What is WebCoRE? (And what was CoRE?)]
Tasker is an android app that can automate various tasks on your phone, auto location is a Tasker plug-in, and Sharp Tools is another android app that links tasker with SmartThings. I’ve not used these apps myself so I don’t know a lot about them, but they seem to be pretty popular around here.