Another beautiful desktop application, this one by David Siegel. I have become a fan of it in the last few months since David started working on it:
Gnome-Do is another very polished application, one that shows a lot of love and care for taking care of the small details. David just released a new version a couple of days ago.
Gnome-Do is inspired by Quicksilver from MacOS and like Banshee, it uses Mono.Addins extensively to make the application more useful:
Go to David's page for more details and screenshots on all the new features (Skype, Flickr, Twitter, IM, Google Calendar integration; community plugins, configuration and more).