This website is created by onlinemc with some html coding and finding all of the eaglercraft clients etc. most of the clients was found and compiled by royaxvirus.
Eaglercraft is real Minecraft 1.5.2 and 1.8.8 that you can play in any regular web browser. That includes school chromebooks, it works on all chromebooks. It supports both singleplayer (only on 1.5.2) and multiplayer.
You can help by becoming a contributor in the github page.
This website uses eaglercraft, it is a version of minecraft built from scratch, only using minecraft free to use textures, noises, and skins
1.9.4 or 1.12 (or both versions)
onlinemc: the creator of this website
royalxvirus: found most of the clients and compiled the offline version of eaglercraft shaders
lax1dude: the creator of eaglercraft
ayunami2000:the current maintainer of eaglercraft
not an easteregg that you probably saw in the code or inspect or with rly rly good eyes