I've not used Slack. How does it differ from Yammer and Jive? I ask, because those two work collaboration platforms have their own valuations. Yammer was bought

I've not used Slack. How does it differ from Yammer and Jive? I ask, because those two work collaboration platforms have their own valuations. Yammer was bought for $1 billion by Microsoft. Jive Software's current market cap is $404 million. I'm curious what the key differences are that drive a $2.8 billion valuation relative to the lower valuations of those two companies.