The simplicity of the iOS lock screen is fantastic, so why not have it on your Mac? Screensaver+ lets you do just that, and you can even set an Android-style unlock pattern for added security.
While OS X's built-in screensaver is perfectly capable of locking down your computer when you step away, if you'd prefer to enter a lock pattern instead of a password you can make that happen with Screensaver+. It'll display a photo slideshow (with photos of your choice, defaulting to OS X's built-in wallpaper collection) and look just like an iOS lock screen until you unlock it. The only downside is that it can be a little slow to start but that's only really a problem when you're testing it. If you prefer the mobile paradigms and want them on you Mac, Screensaver+ will do the trick.
Screensaver+ Free | Mac App Store