Slack, the workplace messaging platform, has announced that it has raised $427m in a new round of funding, giving it a valuation of $7.1bn. The series H equity round comes just a year after it raised $841m.

“The way people work is changing, and we are committed to delivering the best product and experience for our customers in this new era,” it said in a statement.

“We pursued this additional investment to give us even more resources and flexibility to better serve our customers, evolve our business, and take advantage of the massive opportunity in front of us.

“Even with our rapid growth in just four years – we now have more than eight million daily active users and more than 70,000 paid teams – there is still enormous potential to change the way that people and organisations collaborate and work together.”

Slack is the product of Stewart Butterfield’s second failed attempt to make a video game. His first, Game Neverending, had a photo-sharing feature that became more popular; Flickr, was sold to Yahoo for $25m in 2005.

In 2011, he introduced another game, Glitch, in which people cooperated to build a shared world. At its height, the game was costing the company $500,000 a month and bringing in $30,000, so Butterfield closed it in late 2012.

A few employees stayed on to build out the messaging platform that Glitch engineers had used to talk among themselves; that project became Slack.

“Slack’s appetite for funding and its eye-popping leaps in valuation are becoming normal in the private investment market,” reports The New York Times, “where giant funds are eager to write oversize checks to start-ups with momentum and scale.

“In the first seven months of the year, 268 companies raised ‘mega-rounds’ of $100 million or more, a record pace.”

The paper added: “The company has fielded takeover interest from Microsoft, Amazon and Google. When Microsoft introduced its own Slack competitor, called Microsoft Teams, in 2016, Slack took out a full-page newspaper ad offering advice. ‘We’re genuinely excited to have some competition,’ read the ad, signed ‘Your friends at Slack.'”

The lead investors in the latest round were Dragoneer Investment Group and General Atlantic, joined by funds and accounts advised by T. Rowe Price Associates, and funds advised by Wellington Management, and Baillie Gifford and Sands Capital, as well as existing investors.