A Presence and Signaling SDK for .NET. It allows to connect multiple computers in a single conference over the Internet. Of course, a user can be part of multiple conferences at the same time.
Here is a demo (VB.NET)
Free (for ever): Public servers, no SSL (unlimited users, unlimited conferences, unlimited messages, shared bandwidth).
SSL ($800 one time): SSL on public servers.
Isolated Instance ($2400 one time): Dedicated bandwidth, ability to mix SSL and non-SSL users in a single conference.
Contact me by email firstname.lastname@example.org or here https://www.upwork.com/freelancers/~015a6b6dbddab22502 if you are interested.