Five years ago, Slack officially launched out of the ashes of a failed gaming project. Now the company is worth more than $20 billion. From a report: Slack, the workplace communication tool popular in tech and media circles, began trading on the New York Stock Exchange on Thursday, making it the latest tech unicorn to race to Wall Street this year. But Slack took a more unconventional approach to going public. The company chose to list its existing shares directly on the stock exchange rather than raising money by issuing new shares to be sold to public investors. Slack opened at $38.50 a share on Thursday, a more than 50% increase from its $26 reference price -- not to be confused with an IPO price -- set on the eve of its market debut. At that price, Slack has a market value of roughly $23 billion.

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