This site is just a collection of apps and browser extensions where "simple" means simple. Single click. Single tap. No complicated interface. Just the functionality, whatever it is, and nothing more.
We believe any kind of software must be intuitive. And if your app is planned to perform one single action, it should do it with one single button. This site is all about this: one button, one icon, one click, one tap... If an app needs more, it is not listed here.
Some of the apps and extensions listed on this site may have "options" page. This, obviously, may require more clicks. Every app performs it's single function in some default manner, but you may want to customize the way it works. That's why the only exception to the one-click rule is when end-user is changing the given app's settings. Still, this is optional functionality that doesn't break the "single-click" rule.