Steam's annual summer sale is a time-honored tradition at this point, and this year's iteration is particularly monstrous. Users can take advantage of daily rotating deals and flash sales that switch up every 12 hours until June 21st, meaning there'll be plenty of opportunities to find steals even if nothing seems especially purchase-worthy on your first click-through. The sale's kicking off with deals on games like the Tales from the Borderlands series, The Binding of Isaac: Rebirth, and Grand Theft Auto V.
There's also a gamified component to the sale: by playing the accompanying Monster Summer Game, users across the Steam community can work together to unlock even more deals. There are nine possible deals that can be unlocked and accessed each day, tied to joining the game, clicking within it, and defeating boss monsters. One of today's deals, a sale on Crysis 2, has already been unlocked. (The game resets daily, just like the standard sales.) You can check everything out at the sale's main page — and you might want to keep your wallet handy.
Polygon overview: Tales from the Borderlands gameplay