The king of the unicorns?
"In an era of soaring valuations for tech startups, Slack has emerged as one of the industry’s most rapidly-appreciating assets a little more than a year after launching its first product. The startup has more than doubled in value since five months ago, when investors valued Slack at $1.12 billion, and now ranks among the world’s most valuable venture-backed developers of software for businesses.Slack’s Valuation More Than Doubles to $2.8 Billion in Five Months - Digits - WSJ
Unlike many consumer-focused startups with multi-billion-dollar valuations, Slack’s growing adoption among business users is translating into real revenue. The company tries to hook workers on its free service and then convince their bosses to pay for a version with more features."