Office 365 Groups already overlaps with Slack, and has a similar connector model; I'll be surprised if Facebook at Work doesn't also offer similar capabilities. Also see Slack Aims to Become a Control Panel for Your Job (NYT) for more on Slack's platform plans.
"Some observers view such rivals as a threat to the messaging company. “If I were Slack, I’d be worried about Microsoft and Google,” said Gartner Principal Research Analyst Adam Preset. “Either of those vendors has so much infrastructure and talented developers that if they wanted to build something Slack-like, they could do it,” he said.Slack Raises $80 Million Fund to Support Platform Strategy - Digits - WSJ
Although Microsoft in 2012 acquired a similar messaging company, Yammer Inc., for $1.2 billion, Slack has paid more attention to how its software works on mobile devices, Mr. Preset said.
Mr. Butterfield wants to get Slack as widely used as possible, integrating it with business software tools such as Zendesk and Github and creating apps that will make Slack more appealing. Software services for businesses have proliferated so much that there’s “no place where it all comes together,” he said."