Hyperlogout is a website that will log you out from popular internet services that probably implement logout in an unsafe way, such as Amazon, Gmail, Hacker News, Instagram, Spotify and others. See the full list here.
Yes, you've probably seen it before. This is a shameless clone of Superlogout, but you can contribute by adding more vulnerable websites.
We try to trigger logout on your behalf by doing GET and POST requests to some services. If those services don't check whether or not you're manually doing it, they just terminate your session.