Is there a way to close all applications?

[Boesky]

Like close every window you see with one button? Without restarting/shutting down the computer.

 

[BittenApple]

You can close every window inside an App by pressing option while you click the close button or by pressing the keyboard command Command-Option-W

Does not close all the windows system wide but a nice tip.

 

[jmann]

I would just press cmd + tab and keep holding cmd and then press Q a bunch of times to quit all of the applications running.

 

[Gregg2]

Well, Finder is an application also. So, technically, the answer to your question is yes.* But, I assume you mean all applications except Finder. The answer to that is no. I'm afraid you have to quit them one at a time.

*It's called Shut Down!

 

[chriszzz]

You could log out then log back in.