Walking and jumping. Shooting. Having virtual people and things follow you around. These kinds of bedrock mechanics are so ubiquitous in modern video games that it's easy to take for granted that they just work. A new website gives people a glimpse at the mechanics implemented in extremely raw fashion. It's totally charming and enlightening.
Game Mechanic Explorer -- which comes from developer/programmer John Watson -- lets users choose from a bunch of different actions and tweak them with a few variables. Watson also provides the raw code for the mechanics which he built in the Phaser HTML5 game-making toolset.
Now, this is far and away from the engines and programming environments other game developers use for their creations. But Game Mechanic Explorer does give you an appreciation of the scale of complexity that arises in even smaller games. There's a lot of code in there doing lots of little cool things in conjunction with each other.