This is Minecraft Classic: the version of Minecraft from 2009, which Mojang re-released in the browser for the game's tenth anniversary in 2019. It is creative mode only — no monsters, no hunger, no crafting — with the original 32 blocks, the original blocky terrain, and the original bugs left in on purpose. You place and break blocks in an infinite-feeling world and build whatever you like.
It is the one legitimate way to play Minecraft in a browser for free, which is why it is one of the most-searched games on this site. It is not the full survival game: think of it as Minecraft's sketchbook. You can share a link to your world and build with up to nine other people at once.
Yes — it is Mojang's own Minecraft Classic, the 2009 version released in the browser for the tenth anniversary. It is creative mode only, with 32 blocks and no survival features, but it is the genuine game, not a clone.
Not officially. Minecraft Classic is creative-only. Survival mode requires the paid game (Java or Bedrock edition); browser sites that claim to offer free survival Minecraft are running unofficial clones.
Yes. It runs in the browser with no download and is far lighter than modern Minecraft. Click the game once to capture the mouse; press Esc to release it.