Mac: If you're worried less about encrypting your folders, and more about someone accidentally coming across your collection of bad poetry (or, you know, whatever), Obscurity is a simple app that hides away files with ease.
Obscurity is essentially a dummy app. After you download it, pull the Obscurity app from the image into a subfolder (it doesn't work on the dock or desktop), right-click the icon, and select "Show Package Contents." In most cases, this is where your apps hold all their data, but in Obscurity's case this is a dumping bin for all your private files. Drag any files you want hidden into the contents, and you're done. When someone double-clicks the icon, they're shown an empty folder. Better still, when someone searches for a file in Spotlight, nothing shows up. You can always access the files again, by right-clicking and selecting "Show Package Contents."
Obscurity is essentially a clever way to hide your files instead of protecting them. If you're looking for something with a bit more encryption, check out the previously mentioned Skedaddle.
Obscurity | Mednotes via Addictive Tips