Protected Screen is a system security application. It allows you to password your computer by launching an application. The first time that you launch it, it will ask for a password, and you need to verify it just in case you made a mistake when you typed it in. After that, your screen will show your current desktop wallpaper with a text field that lets you type in your password. You won't be able to bypass the screen without entering the password or shutting your computer down. From the lock screen, you can also access the Control Panel. To do this, you type your password and then click on the "Control Panel" button. From the Control Panel, you can change your password, change some options and even choose the background that you want to use when your Mac is locked.
When I tested the app, while the Mac was locked, the space where my dock used to be was flickering. This is not really a problem, since when the computer is locked, I am probably not going to be around to notice this. I was able to lock and unlock my Mac by entering the password.
In short, this is a nice app if you want to momentarily lock your Mac. You can also do this with a password-protected screensaver. But I like that you can lock your Mac by launching an app file, which comes in handy when you use scripts.