SymphonyOS is a Ubuntu-based desktop Linux distribution featuring a custom-built desktop environment called "Mezzo". Written in Perl and Gtk2::Webkit, Mezzo uses the lightweight but highly configurable FVWM window manager to create an unusual and eye-catching desktop user interface with focus on simplicity and usability.
https://archiveos.org/symphony/
https://en.wikipedia.org/wiki/Symphony_OS
https://distrowatch.com/table.php?distribution=symphony