Mac: The sound output on MacBooks is pretty bad, and even when you crank up the volume all the way you can rarely hear anything. Boom is a Mac app that boosts that sound, and it's currently on sale for $4.49, $3 off the usual price.
We've mentioned Boom before, and it does exactly what it's supposed to do. Turn Boom on, and it boosts the sound of everything from videos in your browser to FaceTime calls. It works great, and it's particularly useful on smaller MacBooks such as the Air.