Yes, both Slack and Paymo offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Paymo is designed for Individuals, Freelancers, Large Enterprises, Medium Business and Small Business.
Pricing for Slack Starts at $2.67/Month whereas for Paymo Starts at $4.95/User/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 Paymo includes Quickbase , Smartsheet, ClickUp, Zoho Projects, Wrike, TeamGantt, monday.com, Asana, Teamwork, ProjectManager.com, Microsoft Project, ProWorkflow, VisionProject, Quick Base, Height and Project Insight.