iFuntastic 6.6 beta

iFuntastic is an application for Mac which lets you customize your iOS device's user interface and copy files to and from the device.

Some functionality is available to out-of-the-box devices (custom ringtones (phones only,) use as a USB Storage Device, copying screenshots and wallpaper,) but the really cool stuff requires the phone to be jailbroken (see below.)
You can download the application for free and explore it, but to actually do something useful, you will need to activate one or more feature levels. Activation usually requires a purchase through PayPal (account not required,) but may also be accomplished with promotional activation codes (if available.)