[beej1981]

The space is actually quite crowded. According to IDC, IBM Connections leads the market, not Yammer.

Salesforce, Microsoft, SAP, JIVE, Tibco, VMWare etc. etc. etc. make competing products.

[reagan83]

The IDC analysis report was based on market share of revenue, which placed IBM at the top of the list because IBM has done a great job finding customers to buy their product for more money than Jive & Yammer (aka: Microsoft).

Because social products are much more about engagement and usage vs sales, it would be applicable for IDC to include that metric and weight it heavily in rankings of social enterprise software packages.