Developer: Yammer (it was purchased by Microsoft earlier this year)
Cost: Free for the mobile app; Yammer itself operates on the “freemium” model – for now. The acquisition by Microsoft could change the pricing model eventually.
Available on iOS too? Yes.
Yammer is a secure, private social network for the enterprise. With Yammer, employees are able to collaborate, share ideas and self-organize into teams. Yammer can also be used to improve relationships with customers and partners using one central repository. Yammer will be rolled into Microsoft’s Office cloud effort, filling gaps in SharePoint.