Neave's Snake
Neave's Snake is the Flash rebuild of the Nokia phone game, and it keeps the whole of the original: a snake, a piece of food, and walls that end the run. The arrow keys turn the snake; eat and it grows a segment, and the sooner you reach the food the more the meal is worth.
Three levels set the pace -- SLUG, WORM and PYTHON -- and the board stays as plain as the idea: a light-green field, a dark snake and a score. Pause with P when the tail gets close to its own path.
Neave's own page calls it a back-to-the-roots version, with cheap sound effects and a slight plasticky feel, and that is exactly what it plays like: no power-ups, no scrolling background, just the turn you should not have made.
