Google Hangouts is a great way to carry on a video chat. A group of up to 10 can all participate. Google Hangouts includes the ability to share your screen. This option would allow someone to work from a PowerPoint presentation and all members of the Hangout would see the presentation on their screen.
Here is an excellent video, composed by Martin Shevington, which explains the nuts and bolts of Google Hangout.
Martin Shervington, Law and Business Studies, LLB (Joint Hons), PG Dip Organisational Psychology, Master Practitioner NLP has spent 15 years in this field working as an executive coach, business consultant and marketing psychologist; he is now based between the UK and the USA, dependent upon clients. His website is http://martinshervington.com.