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.
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
MS SharePoint - Share, organize, and discover information with Microsoft SharePoint. Learn about SharePoint Online, OneDrive for Business, and Apps for SharePoint
Anchor CMS - Free and lightweight blogging system
Communifire - Enterprise Social Collaboration Software
Textpattern - Textpattern is an elegant content management system that is free, open source software.