Release notes for all versions going back to version 15.30 (January 2017) are here and downloads to old versions are here. There are also a few features (like ribbon customization) available only to 365 subscribers, though Microsoft doesn’t list what they are they just call them “Premium,” as opposed to “Classic.” (Thanks, Microsoft!) The one-time purchase also gets monthly updates until three years after its original release date, and then two years of security updates and bug fixes (but no new features) after that. In recent history, since 2015 or so, rather than waiting for a single great big new version every few years, Office now receives an update every month, and these updates bring both new features and bug fixes.
Microsoft Office for Mac has been around forever.
