Mac OS. Do you remember it?
It was released 40 years ago, the original Macintosh on January 24, 1984 . So if anyone here answering the question was, say 10 years old when they first used it, they'd be in their fifties now. A bunch of old farts here, on Mastodon. By the looks of things anyway. ๐
Without being funny, is your question serious? As far as I know, macOS 14 Sonoma is the latest version.
I remember using VersaTerm over a modem on System 6 to first invoke FTP to SUMEX-AIM, and then use [xyz]modem to download from the host to my Mac SE.