Mac OS X 10.5 Leopard comes with a selection of entirely new or greatly improved applications. The new system is designed to be flexible to fit your needs, so you can import the data from existing apps you currently use into Leopard's, or alternatively continue to use your own preferred alternative apps on the new OS. It also exposes new functionality for developers to allow them to extend upon, replace, or collaborate with Apple's supplied applications. Here's a look at how the new versions of Address Book and iChat work.