As Elul approaches, I am curious about a list of Seforim that are focused on Teshuva. The starting point, of course, is Shaarei Teshuva by Rabbeinu Yonah. The seforim could be all Hebrew, all English, and could date back all the way from Chazal until today. Thank you!

Note: if someone wants to make a community wiki that works, as I believe many will truly benefit from a list of Seforim on this topic.