Ning.com
What ning.com says about itself: Ning is the social platform for the world’s interests and passions online. Based in Palo Alto, Calif., Ning offers an easy-to-use service that allows people to join and create Ning Networks.

• Flexible Design: you have about 50 templates to choose from and you can add your own navigation and subnavigation quite easily. You can up load your own banner or logo too.
• Member Profiles: Each member has their own profile. You can customize what questions they have to answer which will appear on their profile. They can design their own profile page, upload their photo, add widgets and so forth.
• Moderation: You can make your ning network public or private. You can moderate who becomes a member as well as what they can upload to the network. You can assign rights to members to form groups but also moderate their postings before everyone can see them. You can also set up numerous administrators of the site so managing it can be collaborative.
• Invitations: Members can invite their friends to join by uploading their address book or through .csv importing.  This allows your members to help grow the network.
• Display the Most Recent Activity: Your ning network will display the latest activity for everyone to see - who just joined, who just posted what where or uploaded a photo or video, etc. It's all done in real time, no delay.
• Customization: Administrators can add a text box to pages and then embed a widget (choose from thousands on the web). Text boxes can also just for news, an article, photos, etc. Add as many text boxes as you want.
• RSS Feeds: Stream in or stream out information using RSS functionality. In a public network, all of the features you deploy support RSS feeds. If you are unfamiliar with RSS, visit our page called Learn RSS.
• Photos Feature & Branded Photo Slideshows: You decide if your members are allows to upload and share photos. You can also allow (or deny) members to embed your network's branded photo slideshows on other sites or blogs and link back to your network. Great for promoting membership.
• Video Feature & Branded Video Players: You can also decide if members can upload and share videos, which can also be embedding on other sites.
• Chat: Set up a chatroom so that members present can communicate in real time.
• Groups: Set up your own groups and let members set up their own groups too. They can be topic specific, include images, membership lists, comments, and discussion functionality.
• Discussion Forum: You can set up discussion forums if you want (and let members do that too). Each forum can have "categories" as well as include photos, attachments, and more.
• Blogs for Every Member: You can have your organization's own blog but also enable ning so every member can have a blog if they want one.
• Events: If you have events (virtually or in real time), you can use ning's event feature to announce them. You can also allow members to set up their own events if you wish.