In addition to Overwatch's standard Competitive mode (6v6 capture/escort/control), which is constantly running in consecutive seasons, Overwatch often has limited-time alternate competitive modes available in the Arcade. These modes also seem to repeat, but with large gaps between them.
For example, Competitive Deathmatch's Season 2 is currently running in the Arcade, but I think the previous season was more than a year ago. I think I've played in most of these modes, but I've been wondering which I missed?
What are all of the competitive modes that have been available in the Arcade, and how many seasons has each had?