Windows: LogMeIn Express is a screensharing tool from the makers of the popular remote-desktop software, LogMeIn. Sharing your desktop is as simple as sending your friend or associate a URL.
Only the person doing the screensharing needs to download anything. The sharer only requires a small application from LogMeIn, the viewer only needs to visit the LogMeIn Express site and plug in the number that the sharer has given them.
Once they plug in the number you'll approve them for viewing and — if you desire — remote control. You can send them files, chat with them via the LogMeIn Express control panel, pause the screencasting, disconnect individual users, or shut down the screen sharing all together.
The connection is secured using 256-bit SSL encryption and you can share with up to 100 users. On our test machine no setup or firewall tweaking was required to connect to remote machines and transfer files. LogMeIn Express is free and requires Windows XP and above.