The CW has created a small empire of DC Comics-based shows, and the connected universe comprised of Arrow, The Flash, and Legends of Tomorrow has been a source of all kinds of superhero entertainment over the years.
Arrow, Flash, and Legends of Tomorrow are all set on Earth-1 while Supergirl is set on Earth-38.
Supergirl joined The CW in Fall 2016, but it still remains separate from the other three series as it takes place in a different in a different dimension.