When Jonathan Frazen wrote "Freedom," he did so in a spartan, rented office on an old Dell laptop that he rendered impossible to connect to the Internet. He not only removed the laptop's wireless card, but he also permanently gummed up the Ethernet port. He told Time magazine, "What you have to do is you plug in an Ethernet cable with superglue, and then you saw off the little head of it."
I don't recommend going to such extremes on your work computer (unless you are working on the next great American novel), but who couldn't use a little extra help focusing on work, with the great distraction that is the Internet only a click away? With HazeOver, you can highlight your Mac's active window while dimming all other distractions lurking on your desktop. HazeOver costs $3.99, £2.99, AU$5.99 in the Mac App Store.
When HazeOver installs, it places an icon in the menu bar. From its menu bar button, you can toggle HazeOver on and off. You can also use the cumbersome keyboard shortcut Option-Shift-Command-H to toggle the app.
Also from the menu bar, you can use a slider to adjust the opacity of the dimmed background, from barely noticeable to nearly opaque. In preferences, you can also use a touchpad gesture to adjust the level of dimming. Elsewhere in preferences, you can set it so only the front-most window is highlighted or all front windows from the active app are highlighted. And for multiple monitor setups, there is a check box to highlight windows on the active display only.
If you are happily focused and productive using HazeOver but need to drag and drop a file on your desktop, you can temporarily disable dimming by holding down the Fn key while dragging.
Before you glue the head of an Ethernet cable to your MacBook's network port and rip out its wireless antenna, give HazeOver a try first.