Web conference software?

I can't believe it's been more than a month since I posted something here last time...

I have a sort of random question.
What is a good free web conference software? and I feel like this is mentioned in one of today's tech talk. I some times use Skype but I need something else because Skype is only used for one-one web conversation, not for multiple people talk. I need this function because I have this group of Japanese conversation practice ,that I facilitate weekly in the semester and want to continue doing it even in summer when many people are out of town. I am thinking of maybe having one hour session per week where people can participate online using a software like skype except with no limitation of the number of people. What's the best way?

I guess I'll start looking right now...