Yes, both Slack and Commented offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Commented is designed for Large Enterprises, Small Business and Medium Business.
Pricing for Slack Starts at $2.67/Month whereas for Commented Starts at $7.40per month when Billed Yearly.
Some top alternatives to Slack includes Microsoft Teams, Glip, Google Chat, ChatWork, Dialog, Office Chat, imBee, Takle, SPACE Channel and Teamwork Chat.
Some top alternatives to Commented includes and undefined.