This one subverts the entire video game industry in one step. Your goal is to kill your main character. This is actually a sequel, but you might as well play the latest version since it has only improved upon the first.

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The premise is that you need to help your salesman and any other characters on the level kill themselves. This usually means figuring out a way to jump onto some spikes. This means running, jumping, flying, flipping levers, etc. This version takes it a step further and features a lot of puzzle aspects that aren't just in the game. You need to do special things, like clicking on the link to their website, finding the secret spikes in the fake credit screen, completing a level with only 5 jumps, understand some weird settings, etc. This makes for an interesting and challenging experience.
It's just a fun game overall. Check it out here.