If you are into machine code, here is Space Invaders, one of the first Arcade games, including TILT.
Paul Bakaus thinks that GIFs must die.
You can find your name in Pi in Dr Mike's Math Games for Kids.
If PICO-8 is too limited for you: microStudio is a free game development environment for the LUA programming language.
Matt Webb found a very early shopping list ... app?