They both don’t make a direct competitor, as Asana is majorly focussed on Project Management, while Slack brings team conversations together. Nearly both tools have made their launch to the public in the years of 2012 and 2013 respectively.
Asana has its foothold across a wide number of customers globally. The clientele-stack of Asana is fully loaded with big names of diverse industries such as; Nasa, Google, Bill & Melinda Gates, foundation, yelp, Vodafone, Deloitte, Avon, The New York Times, Airbnb, Uber, and the list goes on. Founded by Dustin Moskovitz and Justin Rosenstein as a Software-as-a-Service project management tool with the most recent valuation of $1.5B.
Check here to choose which one is better for communication: Slack Vs Asana