Espionage is a very simple but powerful tool that allows you to encrypt files and then use them directly in Finder. It's designed to replace FileVault.
The advantage of Espionage is that it allows you to encrypt individual folders and interact with them directly in Finder with no need to encrypt your entire hard drive or create an encrypted partition just to protect its contents. Espionage also gives you far more control than FileVault by specifying which folders you want to encrypt instead of your entire Home folder. The big advantage of using Espionage over Disk Utility is that it merges the disk image and the mount point together into a 'folder', which means things like encrypting your email is possible and all-round data securing is more straightforward.
Using Espionage is a bit tricky at first though and it would have been helpful to have had some kind of setup wizard from the start. In addition, some people may not like the way the encrypted folders it creates are actually bigger than the original. Therefore, make sure you've got plenty of disk space free if you're encrypting several large folders.
If you want to quickly password protect a folder from prying eyes, Espionage is a flexible and fairly straightforward solution.
