Yammer is a leading Enterprise Social Networking platform used by over 200,000 organizations worldwide and it has been described as a "Facebook for business". Yammer was launched in 2008 and is recently acquired by Microsoft.
This is how Yammer will be offered as part of Office 365 in March next year:
- SharePoint Online (Plan 1) + Yammer Enterprise $4 per user/per month
- SharePoint Online (Plan 2) + Yammer Enterprise $8 per user/per month
- Office 365 E Plans 1–4 + Yammer Enterprise $8–$22 per user/per month
Also check Yammer pricing here: https://www.yammer.com/about/pricing/