I just saw this over on Free Technology For Teachers, and after some brief experience with it here in the College of Education, I decided to post it. The program seems to be very straight forward, and very simple to use. With Join Me, a presenter can send the audience their code and then simple share their screen with them. The great thing is that it works with Mac and PC. Also, the set up is very easy, with no pre-installation required. I set up eight computers to use this a few weeks ago, and they all worked fine. Definitely worth a look.