It's been almost 60 articles since I wrote about using screen sharing, back in Tech Bit 7. Since then a lot has changed.
Back then, there were very few free options, the one I mentioned was Vyew, www.vyew.com. It is still available for free, with a 10 person watching limit, and has the advantage of being entirely web browser based. It can also support both VoIP and a Webcam to let your viewers see and hear you.
Another, new option, is Join Me, www.join.me. It is free also. It's also very new, so it's not clear what limitations there are. It works with both PC and Mac operating systems and not only allows screen sharing, but remote control (handy for tech support), and file transfer. It uses an audio, call-in type communications (or on-screen chat), much like freeconferencecall.com. It does require a download for the presenter, but viewers don't need any software installed on their computer. Once you are connected, another person can request control of your computer. I'm typing this part of the article from another computer in our network. It does not appear that you can send an invitation to join.me then take over the other person's computer (e.g. to diagnose their computer), they would have to initiate the connection (still a nice way to help a friend).
The other new option is from the people who offer free conference calls, freeconferencecall.com. Freesee, www.freesee.com, is targeted more at a webinar audience than sharing your screen with a just a handful of people. Freesee's current limit is 96 attendees, but I'm told that will increase to almost 1,000 in the future. It requires a software download for the presenter, but none for the attendees, and works with both PC and Mac operating systems. It has most of the same features as Join Me and Vyew, including application sharing (of course since PowerPoint is an application, you can "share," aka display, your slides). One limit I did notice is that you can't stream video, so I presume that embedded videos in PowerPoints will not be seen by attendees.
The possibilities for screen sharing to make conference calls more productive, by keeping the attendees focused on the agenda and notes, and for doing webinars or remote training, make these free options very exciting.