I've been using Slideshare for awhile to post and share my presentations and technology tutorials. It is a free tool and is an excellent way to share knowledge that might be otherwise hard to access once a presentation at a conference or meeting is over. I also find the site helpful to learn from if I need to learn a topic quickly, as there are many presentations on almost every topic available on the site.
Recently, I learned that Slideshare has introduced something called Zipcast, which is a free meeting tool. It provides the user with personalized meeting rooms, group chat, streaming live video, and Facebook/Twitter integration. You can login to a meeting with either a Slideshare or Facebook account. If you upgrade to their paid option, Zipcast Pro, you are able to use Zipcast without ads, use password protection and access a conference number. But I think most will find the free option to work just fine as long as you have your own conference number to use.