Yes, both Segment and Slack offer a Free Trial.
Segment is designed for Large Enterprises, Medium Business and Small Business.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Pricing for Segment Starts at $120/Month whereas for Slack Starts at $2.67/Month.
Some top alternatives to Segment includes CustomerLabs CDP, BlueConic, Captain Metrics, Zylotech, Lexer, Acquia Marketing Cloud, BSI CDP, Gravito CDP and euromessage CDP.
Some top alternatives to Slack includes Microsoft Teams, Glip, Google Chat, ChatWork, Dialog, Office Chat, imBee, Takle, SPACE Channel and Teamwork Chat.