Various Command Line Interface tips and tricks
Some of the things at Ubuntu are Ubuntu Linux specific, some of them will work on other systems, including in the MacOS Terminal.
lsof -i :8080
Will list what's running on port 8080.
Looking up the process ID (PID) means you can get more info, or
kill [PID] to shut it down.
See also: Daniel Miessler's An lsof Primer (2019)