Windows/Mac: Mikogo sports the basic features you'd expect from a decent desktop sharing tool: whiteboard functionality, mouse pointers for participants, and remote control. Where Mikogo shines is one-click reversal; you can nearly instantly switch from the current desktop to a viewer's desktop.

Mac OS X: ScreenSharingMenulet gives you easy access to local, remote and Back to My Mac VNC servers directly from your OS X menubar. It's customisable, lightweight and completely necessary if you make heavy use of VNC.

Windows/Mac: Join.Me is a free tool from the creators of LogMeIn. Download the app, run it, share the URL with a friend and you've got nearly instant screen sharing with text chat, voice conferencing, mouse sharing and more.

Linux: Skype doesn't update its Linux beta too often, but good things arrive when it does. This go-round, screen sharing gets added to the mix, interfaces can be styled, and a lot of annoyances were chopped down.