GoToMeeting. It's wildly under-utilized.
Yes GotoMeeting, GlobalMeet, Joinme, and others. I trained 244 people all over the country about a week ago using Globalmeet-Webex. Last year I trained 440 at once.
Not just colleges, public schools could resort to it too. Conventions, corporate trainings, business meetings could all use it to reduce exposure. Heck if you could sufficiently secure it, Congress could probably use it too.