OS X: Macs still shockingly lack a native screen locking feature. Luckily, QuickLock is a simple app that brings this much-needed functionality to OS X.
Mac users hoping to lock their systems have long-needed to use a workaround that involved putting the display to sleep and immediately requiring a password, but QuickLock is much more intuitive. Once installed, you can lock your system by clicking a menu bar icon or keying in a custom keyboard shortcut, and you can unlock it with the password of your choosing. One delightful touch is that you don't have to hit enter after keying in your password; your Mac just unlocks instantly.
The app ships with a few bonuses too. You can customise the lock icon to your liking, add your own background and even see what song is currently playing in iTunes. QuickLock is a free beta available from the developer's website.
QuickLock Beta [Inertiactive]