Lockdown?

I haven't seen/heard of an app that'll do this. Some apps, though, do have features where you can set passwords to whatever the app may be used for. For example, the app Note Everything Pro allows you to put a password on any and all notes you want. I also know of another app (can't remember the name) that lets you place certain pictures under password protection.

If you come across an app that can set passwords for every other app, then please let me know.

 

I think I've scoured the Market looking for various security apps, including an app like you suggested, but I haven't found it.

EDIT:
I just found an app called B-Folders, that can secure your contacts, folders, notes, credit cards, log-in passwords, and bookmarks that you want to keep private. You need to set a master password for the app when you first install it.