When it comes to platforms, check out Grou.ps (http://grou.ps). I have just started trying it out my self in a model where I as a teacher in HE use Drupal as a space where I'm "the boss". I would like it to work like a versatile blog/CMS where students can meet me and get information, and not only during a course. Call it my virtual office, if you like. Grou.ps again would work as a more collaborative and democratic environment connected to a certain course. There would of course be a lot of hyperlinks between the two.

Grou.ps is open source, free and ad-free. It was the ads (alternatively a relatively high monthly fee) that made me stop using Ning for this purpose.
Grou.ps is still a little rough around the edges but very flexible and it seems to develop nicely.

Cheers,

Romi