Slack is a collaboration platform for enterprise customers that works both in browsers and on mobile devices. The nearly 2-year-old company released its first transparency report on Friday. Slack

Slack Technologies Inc. is quickly rising up the billionaire startup chain. The online workplace collaboration tool is reportedly raising $160 million at $2.76 billion valuation in its latest funding round.

This report, from the Wall Street Journal, continues to support a Bloomberg estimate that Slack has reached an over $2 billion valuation. In October 2014, the company was valued at $1.12 billion.

Those are impressive numbers for a company that launched its main product publicly in February 2014. It means Slack has solidly joined the club of so-called "unicorns," private startups worth a $1 billion or more. Slack declined our request to comment on the latest funding.

Currently with over 500,000 million daily users, Slack has become a dominant messaging platform in tech and media industries and has shown unprecedented user growth.

Unlike some other companies which have been valued at $1 billion without existing revenue models, such as Instagram, Slack has both a free and a paid version. Over 135,000 of its 500,000 users pay a monthly fee.

So far, Slack has raised $340 million. Horizon Ventures, a Hong Kong-based investment firm, is said to be leading the latest round with a $50 million contribution. Not that the company needs more money. Slack co-founder and Chief Executive Stewart Butterfield is quoted by the New York Times saying the company has “a lot of money and not a lot to spend on.”