Deloitte predicts over 90% of Fortune 500 companies will have partially or fully implemented an enterprise social network by the end of 2013.
(Yammer's pricing page lets you chat in real time with reps, who respond quickly to any inquiry you may have.) VMware's Social Cast is another ESN optimized for mobile or desktop.
It provides a centralized workplace and communication center for employees.
The profile layout is similar to Facebook, with space to list professional skills, past projects and people you've worked with.
You can follow topics, people, apps and project updates, then see who else follows similar subjects.
The UI is also similar to Facebook, with status updates, pages and "follow" capabilities.