Chat rooms are a communication medium particularily popular for real-time communication over wide distances and culltural borders. In open source development where people collaborate from different time zones, cultural backgrounds and mother languages, chat rooms based on IRC have established as the second most important communication medium next to mailing lists.

Another alternative to chat rooms are web conferencing systems, but this is an own class of applications that comes with a different usage profile. 

Advantages of Chat Rooms compared to Mailing Lists

• Shorter response time
• Real-time chat
• Ability to ask back more easily

Disadvantages of Chat Rooms compared to Mailing Lists

• No threaded discussions
• Limited number of participants before room becomes too crowded
•  Most chat rooms have no proper logging, makes it hard to refer to older conversations

Advantages of Chat Rooms compared to Web Conferencing

• Written languages leads to more concise understanding
• A conversation is not grabbing all the attention of the participants
• Possible number of participants is higher
  

Disadvantages of Chat Rooms compared to Web Conferencing

• No audible or visible feedback of chat partner's emotional context
• Weak support for media sharing