If you use Gmail, you have probably had one or another moment where you wish you could take back the "send" click. Gmail now has an undo. Click on the tiny green beaker icon on the top of your Gmail page to open the Google Labs department for Gmail. Scroll down, or search for "undo send," and enable it.

Reload Gmail, and now, when you click send, you will gain a 5 second window to click "cancel" at the top of your screen. That will often be enough to catch those unavoidable "oops" moments. Try it on a test message to yourself. It works.

If you have never visited the Labs department of Gmail, take a look at some of the other features there. We consider them safe, just not necessarily what Google has decided are desirable permanent features or in permanent form, so the remain in the Lab. To be safe, introduce them one at a time to make sure you understand their effects.