If you want to share a cool game on your iOS device but not let everyone read your email, Locktopus offers a simple app-by-app lockdown solution.

Locktopus is a super simple application for jailbroken iOS devices. Install the app from the BigBoss repository through Cydia, go to the system menu and set a password--more specifically, change the default from "password" to something a little more clever--and then tap and hold any application icon on your springboard screen as though you wanted to move or delete it. When the icons begin to vibrate and the little delete X appears in the upper corner you'll have a new addition, as seen in the screenshot here, of a small lock icon. Tap the icon to lock the app. From that point forward every time someone attempts to launch the app they'll have to enter the password.

It's a great app for keeping your private stuff private--email, instant messages, medical apps--and for setting up a device for a child to use. You can lock down, for example, Safari, Settings, and YouTube to keep them from getting into trouble online but keep them easily accessible for the adult users. Hit up the link below to read more about it and then visit the BigBoss repository via Cydia on your jailbroken iOS to install it. Locktopus is $2, a large sum to pay for a feature that should have been included in iOS but a small sum to pay for such a handy application.

Locktopus [BigBoss Cydia Repository]