Eaglercraft 1.5.2 offers a surprisingly complete Minecraft experience that runs entirely in your browser:
Despite running inside a browser tab, Eaglercraft offers a surprisingly robust feature set that mirrors the authentic desktop experience. 1. Full Singleplayer Experience eaglercraft 15 2 unblocked free
Because it runs on HTML5 and WebGL, it runs smoothly on almost any computer, including low-spec laptops and Chromebooks. Eaglercraft 1
If your school network blocks every available website, you can download the game to run entirely offline: eaglercraft 15 2 unblocked free