Cobalt Strike is a framework for penetration testing. Allows you to generate payloads using the built-in encoder and use them for exploitation and post-exploitation of vulnerabilities, securing and controlling the target network.
It was created in 2012 as a legal framework for conducting security tests of computer systems and networks. It is a commercial product, the free trial version has much reduced functionality.
Simplicity and ease of use contributed to the popularization of Cobalt Strike in the cybercriminal environment.