If you own one of the smaller MacBooks, you've undoubtedly cursed their quiet speakers hundreds of times for being inaudible when you really need them. Boom is a menu bar app that will boost your Mac's volume past its default maximum point.
Whether you have a video that's just too quiet or your computer's speakers aren't quite loud enough for everyone to hear, Boom can fix the problem. Just install it, and when your max volume isn't enough, head to Boom's menu bar icon and crank up the volume. It also has a built-in equaliser, and can boost the volume of certain files if the files themselves are too quiet — though I don't recommend this, as it often introduces quality issues to the sound. It's a great app for its system-wide volume boosting alone, though, and if you have a speaker-crippled Mac, it's a must-have tool.
Boom is a $US6.99 download, though you can try it for seven days before you buy.
Boom [Mac App Store]