Dr. Z and I just got done experimenting with Yugma, a new screen-sharing and web conferencing service that's free and web-based. I'm pretty excited about it.
Like many Web 2.0 tools, Yugma requires a login, but registration is free and simple (one only need provide a name and valid email address). With an account, a user can either begin a new screen sharing session or join an existing session from the Yugma home page. Sessions can involve up to 10 users for the free service (up to 500 for a premium account). Inviting someone to join a session is as easy as sending an email (which the web site helps you do, of course), and joining a session only involves logging into the service and entering a 9-digit session ID number. By the way, Yugma works with Macintosh, Windows and Linux PCs, so it's cross-platform. It does, however, require a recent version of Java software be installed.
Once participants have joined a session, they can view each other's screen (not just PowerPoint--anything on the screen), share control of a screen, draw on it, text chat, and even dial a phone number to conference call (it's not a toll-free number, but cell phones and Skype work great for this). If you combine a Skype video chat with a Yugma session, then you've got two-way video and audio as well as screen sharing.
Basically, Yugma--a free solution--provides all of the functionality used in all of the webinars that I've recently attended. It's really quite easy to use and I'm impressed with the clarity of shared screens. This is fantastic for tech support, web conferences, distance education, and many other situations. I think Yugma just edged out Jing as my favorite tech tool of the week.