Regolith packages preconfigured i3wm (and now Sway) alongside basic utility apps (file manager, image viewer etc.) and GUI configuration manager. Notifications and similar stuff, which you have set up manually in some window managers, works out of the box. I’d call Regolith a full blown desktop environment. Too bad it’s intertwined with apt so much, so porting it to distributions other than Ubuntu and Debian is complicated.