You may be thinking of Hackpad from 2014, which later was bought by Dropbox and morphed into Dropbox Paper. I guess I was thinking that a multiuser IDE is substantially different than a multiuser text editor. I did notice that Zed is by the same team that brought us tree-sitter, which is a wonderful innovation that many text editors are now using to good effect. I was wondering if were powerful enough for one person to be debugging some code in the same session that another person was refactoring.