Mac OS X,  Ubuntu,  Windows XP

Cross Platform Screen Sharing: TiffanyScreens

Sure, you can screen share using ARD – but to Windows? TiffanyScreens is a little application that can run on Mac, Windows or Linux. It allows you to share your screen to a number of client systems, very useful with presentation broadcasting, training and standard screen sharing. I’ve tested in my lab with Windows 7 and Snow Leopard and must say that I’m impressed by how well it shares screens and how zippy it is over my AirPort network. Nice little app that deserves a plug:
http://www.tiffanyscreens.com