Yes, both Slack and Unifize offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Unifize is designed for Large Enterprises, Medium Business and Small Business.
Pricing for Slack Starts at $2.67/Month whereas for Unifize Starts at $40/User/Month.
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 Unifize includes Flowist, CollaborateCloud, Genialcloud Facsys, Breakout, Qualified, Workvivo, Flowall, Pascal Workflow, Dashpivot, IFTTT and Consider.