Snake an old arcade game concept, originating in the game "Blockade" from 1976. It's been released under many different names, but I prefer Snake. Below is a version that allows you to see the source code of my incarnation of Snake and play it, but there is a full page version as well. Just hit the play button above the code to start.
You can use the arrow keys to move, but that might move the page as well so I recommend using WASD. Clicking on the settings button reveals some settings, including how many squares the grid should contain, how big each square should be (in pixels), the speed, which is measured in milliseconds between each movement, and the amount of segments each food item gives you. See if you can beat my high score of 92 with default settings!