Blots

Blots is a really simple app that lets you place a black mark over any part of your screen so that if someone else happens to be looking at your screen, they'll have no idea what's underneath the mark.

The options in Blots are extremely basic. You can choose between a square, rectangle, circle, or oval. Once you choose one of these shapes, you just have to select one and drag it to the other side of the screen. The most common use for this app is to cover the name or telephone number of the person you're chatting with.

Blots is a 'censorship' app that, while pretty basic, lets you hide certain information from any prying eyes. Although, of course, the faster (and probably more effective) option would be to tell whoever's looking to just stop.