A few recent ones and some which seemed to have missed a mention
Google talk
The best way to get in touch with your friends.
you can chat call the other person if you have a headphones with mike, and
since it is from google its absolutely free. Google talk is based on the XMPP
protocol which is an open standard. You can also connect to googletalk using
any other third party clients which supports jabber/XMPP.
Download: http://www.google.com/talk/
Google Sketchup Free
Google SketchUp (free) is an easy-to-learn 3D modeling program that enables
you to explore the world in 3D. With just a few simple tools, you can create
3D models of houses, sheds, decks, home additions, woodworking projects -
even space ships.
Website: http://sketchup.google.com/
Download: http://sketchup.google.com/download.html