Yammer began as an internal communication system for the genealogy website Geni.com and was launched as an independent product in 2008, then acquired by Microsoft Corporation in 2012.
Yammer is a freemium enterprise social networking service established to foster team collaboration, empower employees, and drive business transformation.
Currently Yammer is included in all enterprise plans of Office 365 and Microsoft 365.
The service allows employees to collaborate in real-time across departments, geographies, and business applications. Moreover, it helps them to create groups to collaborate on projects and share and edit documents.
For additional information, visit their official webpage.