While macOS is currently on version 11 (otherwise known as Big Sur) and macOS 12 Monterey is coming later this year, there are plenty of folks who use old versions of the Mac operating system. Some people are still using OS X 10.7 Lion and OS X 10.8 Mountain Lion, and until recently, you had to pay Apple $19.99 to get download codes for those OSes. But there’s good news: Apple is now offering Lion and Mountain Lion for free for anyone who wants them.
You can snag Lion here and Mountain Lion here.