Diaspora: Although in its Alpha this platform lets you share whatever you want with whomever you want and you can even host your own server!
From their site:
These resources are taken from Deltina Hay’s critically acclaimed book, The Social Media Survival Guide, already in its second edition. Social Media Power readers can get a discounted copy of the book from the publisher. Learn more about Deltina and her availability for speaking engagements at Deltina.com. You may also enjoy listening to her video tutorial series on YouTube.