Yes, both Slack and Accelo offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Accelo is designed for Large Enterprises, Medium Business and Small Business.
Pricing for Slack Starts at $2.67/Month whereas for Accelo Starts at $24/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 Accelo includes Quickbase , Smartsheet, ClickUp, Zoho Projects, Scoro, Wrike, ManagePro, Asana, Teamwork, ProjectManager.com, ProProfs Project, Microsoft Project, GanttPRO, ProWorkflow, ProgressBoard and Quick Base.