Continu

Continu is a small and simple to use OS X menu bar based app that makes sure that one or more applications will always be running on your Mac. If they crash or should accidentally be closed, Continu.app will automatically launch them again, either giving them focus or opening them in the background. Continu.app can also add a parent to an application which means that the application will only be launched or relaunched when the parent gains focus.