Bitrix24 - Bitrix24 is a free (for small businesses) social enterprise platform. It is a united work space which handles the many aspects of daily operations and tasks. Create your own social intranet in minutes!
Yammer - Yammer is a leading enterprise social network used by more than 200,000 companies worldwide, including 85% of the Fortune 500, to get work done smarter and faster. Sign Up Today.
MS SharePoint - Share, organize, and discover information with Microsoft SharePoint. Learn about SharePoint Online, OneDrive for Business, and Apps for SharePoint
MangoApps - Founded in 2007, MangoSpring transforms the way teams work together.
Communifire - Enterprise Social Collaboration Software
Blink - Blink is a team and employee app, with a Feed, Chat and Hub (for documents, links, files).