Yes, both Slack and Zoho Desk offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Zoho Desk is designed for Large Enterprises, Medium Business and Small Business.
Pricing for Slack Starts at $2.67/Month whereas for Zoho Desk Starts at $7/user/month when 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 Zoho Desk includes Zendesk Support, Tidio Helpdesk, ManageEngine ServiceDesk Plus, Jira Service Desk, HelpDesk, SysAid, Desky, ReadyDesk, Sitehelpdesk, Trakdesk, HESK and BoldDesk.