The remake of Spelunky made waves and won awards when it landed on Steam, Xbox Live Arcade, and PlayStation 4. You can play the original for the low, low price of nada in your browser or as a Chrome packaged app.
Spelunky HTML5 is another platform game that requires you to jump, duck, crawl, whip, and climb your way through danger toward greater and greater treasures. Even better, the dungeons you crawl are randomly generated, allowing the game to present a unique experience each and every time you play. (The controls take some getting-used-to, so check out the tutorial level before playing.)