Synchronous Tools

Synchromous tool enables real-time communication and collaboration in a "same time-different place" mode. these tools allow people to connectat a single point in time, at the same time. Synchronous tools possess the advantage of being able to engage people instantly and at the same point in time. The primary drawback of synchronous tools is that, by definition,they require same-time participation-different time zones and comflicting schedules can create communication challenges. In addition, they tend to be costly and may reqsuire significant bandwidth to be efficient. 

Tool	Useful for	Drawbacks
Audio conferencing	Discussions and dialogue	Cost, especially when international participation is involved
Web conferencing	Sharing presentations and information	Cost, bandwidth; may also require audio conferencing to be useful
Video conferencing	In-depth discussions with higher-touch interactions	Cost, limited availability of video conferencing systems
Chat	Information sharing of low-complexity issues	Usually requires typing, "lower touch" experience
Instant messaging	Ad hoc quick communications	All users must use compatible system, usually best for 1:1 interactions
White boarding	Co-development of ideas	Cost, bandwidth; may also require audio conferencing to be useful
Application sharing	Co-development of documents	Cost, bandwidth; may also require audio conferencing to be useful

Resource :  http://www.asaecenter.org/Resources/articledetail.cfm?itemnumber=13572