Slack confidentially files to go public

New York (CNN Business)Slack, the popular workplace communication platform, has filed confidential paperwork to go public. Slack CEO and co-founder Stewart Butterfield is known for saying the company is opportunistic about capitalizing on people’s interest in the service — whether it’s from investors wanting to pour money into the company or expanding Slack into new countries. The company has been vocal about accepting new investment, even when it has yet to tap the vast majority of money in its warchest. To date, it has raised about $1.2 billion from investors including SoftBank and Accel. In August, the company was valued at $7.1 billion. Slack’s messaging service helps employees better collaborate on work. It’s been called an “email killer,” providing users …