You can place handy little app widgets in the Notification Center sidebar on your Mac. Included with El Capitan are widgets like stocks, weather and a calculator. You can also purchase new widgets from the App Store.
Gary Rosenzweig takes a look at some alternative to the Dashboard Widget calculator that ships with Leopard.
Gary Rosenzweig looks at all the cool news features in Dictionary with Leopard. You can look up definitions, thesaurus entries, a special Apple dictionary, Wikipedia and Japanese dictionaries. You can also see dictionary front matter and look up words while in other applications.
Gary Rosenzweig takes a look at Google Gadgets new compatibility with Mac Dashboard Widgets.