Mac: Wolfram Alpha is packed with a ton of great info, but it's easy to forget about it sometimes. Nimble is a little menu bar app that will stuff that search engine into your Mac's menu bar. Nimble works pretty much exactly as you'd expect. Just click the menu bar icon (or tap Command+Shift+=), type in your search and Nimble dishes out the result in a small window. As far as we could tell, Nimble can handle pretty much anything you'd normally throw at Wolfram Alpha, including simple questions and maths problems that require graphs.
Nimble (Free) [Made by Bright]