Nautilus Actions - advanced custom actions in Nautilus

"Nautilus-actions is an extensions for nautilus which allow to add arbitrary program to launch through the nautilus popup menu of selected files. Each time you right-click on one or several selected files in nautilus, nautilus-actions will look at its configured actions to see if a program has been setup for this selection. If it is the case, it will add an item in the menu that allow you to execute the program on the selected files."

Nautilus already has the builtin support for customization with scripts, but the Nautilus Actions extension takes this a bit further.