Schoolbreak.io is a browser multiplayer game with a school setting: you join a shared world with other players and compete in whatever the mode calls for, with the instant entry and no-install access that defines the .io genre.
It's built for the exact situation its name implies — something to play in a short window on a machine you can't install anything on.
Yes — it runs in the browser with nothing to install and no account required.
Yes — you share a lobby with other players in real time.
Yes — a light .io game with nothing to install.