Pwny is an implementation of an advanced payload written in pure C and designed for portability and extensibility. It is designed to provide an advanced and extendable interface between attacker and target device.
From the beginning there were multiple ways to provide this interface, most common one is reverse shell which gives attacker ability to execute system commands on target system. However, when it comes to exfiltrating data and executing more complex tasks, reverse shells become useless. Thats why the idea of creating Pwny appeared.