I'm looking for a system that is similar to an online classroom setup but allows for virtual meeting rooms with video/audio conferencing, and of course file sharing. I'm preferring an open source solution that I can edit/tweak myself as needed, and is of course free.

Ultimately, I guess what I'm looking for is something that we could possibly tweak to give our own "branded" look and feel, if possible, along with full integration within our own servers. Thus the reason I brought up open source solutions.

Do you masters of the web know of such a system available? If so, do you have a preferred one that you would suggest? OR, can such a system be developed by slapping together a couple of open source projects to derive at what is desired?

Thanks for sharing your expertise.

(FYI - I am a developer that is comfortable with PHP and C#. I'm not experienced with Ruby or Python, but a system using them or something else is acceptable. We can figure it out I'm sure.)