Business software pioneer Salesforce.com is buying work-chatting service Slack for $27.7 billion in a deal aimed at giving the two companies a better shot at competing against longtime industry powerhouse Microsoft.

The acquisition announced Tuesday is by far the largest in the 21-year history of Salesforce. The San Francisco company was one of the first to begin selling software as a subscription service that could be used on any internet-connected device instead of the more cumbersome process of installing the programs on individual computers.

Salesforce’s CEO Marc Benioff hailed the “cloud computing” concept as the wave of the future to much derision initially.

Salesforce has been building on its success in recent years to diversify into other fields, largely through a series of acquisitions that included a $15.7 billion purchase of data analytics specialist Tableau Software last year.