Is there a WPMU product that works like P2?

I am a WPMU rookie so forgive the rookie questions. I need a simple collaboration tool for an upcoming school I am running. I need all the instructors and students to have a fast, open documented discussion / collaboration. I was planning to use the WP P2 theme because of it's simplicity ease of use. However. I can't seem to find a way to make it work well on mobile devices. The sidebars disappear loosing the categories and tags benefits.

Then I recently became a WPMU member and now have access to all of these awesome WPMU products. Since I haven't used any of them yet, I'm wondering if any of them will do what I need. Ive watched all the videos , read docs, and searched for all the YouTube tutorials and still can't seem to find the answers I need. I thought I'd ask the question here and hopefully get some help.

This is what I I am hoping to do with WPMU tools:

1 - A simple uncluttered or complicated collaboration tool like P2. It has live twitter like discussion on front page, sorted by category, tags, ect.

2 - It needs to be private.

3 - I want all those functions to work on mobile devices.

Everything I have reviewed on WPMU looks more complicated than P2. Since I have not ever used P2 or any WPMU product (yet) I know someone out there knows how this can work. Any help is GREATLY appreciated. Thanks!