(Windows and Mac; free trial, then $10 to download)
Freedom takes an all-or-nothing approach to battling online distractions -- it disables your computer's networking capabilities, blocking the connected world for as little as 15 minutes or as long as 8 hours.
The tool is not entirely heartless -- an option at startup lets you remain locally connected, handy if you still need access to your company's LAN, for example.
Once running, the program doesn't remind you that it's there -- the small Freedom button remains unresponsive when clicked. That's because, once you fire up Freedom, it cannot be disabled -- save by rebooting your entire system. Drastic, perhaps, but effective, or so say a handful of famous authors.