Catchr is an iPhone app that logs everything people are doing on your iPhone while you’re not around. For instance, say you don’t have your iPhone passcode-protected and you set it down and walk away.
If your buddy decides to snoop around your device, you will know exactly what they did: which apps they opened, which apps they looked at, what they closed, etc. It also lets you know where your phone has been and when it was moved. Pretty cool stuff.
That said, it won’t work with two of the iPhones apps: Mail and Phone. That’s more due to App Store developer rules.