Windows: It might not be the fastest way to launch apps, but OS X's Launchpad is intuitive and easy for everyone to understand. If you're hoping to get the same feature on your Windows machine, WinLaunch is the solution.
Once you install WinLaunch, you can assign it to a hot corner, your middle mouse button, the default Shift+Tab keyboard shortcut, and a few other options. No matter how you choose to launch it, once you do, your desktop will fade away to make room for a Launchpad-like grid of applications. Just like Launchpad, you can organise your icons onto different pages and drop them on top of each other to create folders.
Unfortunately, the launcher doesn't auto-populate with all of your applications on first launch, so it'll take a little work to get up and running. Once you do though, it's every bit as fluid and responsive as Apple's version.
If you're reading this site, you probably know that this isn't the fastest way to launch apps on Windows (that prize belongs to Launchy). It is dead-simple to understand though, so even if it's not your cup of tea, this is a great app to remember when you're helping less tech-savvy friends set up a new computer.