Yes, both Slack and Sine offer a Free Trial.
Slack is designed for Freelancers, Large Enterprises, Medium Business and Small Business.
Sine is designed for Large Enterprises, Medium Business and Small Business.
Pricing for Slack Starts at $2.67/Month whereas for Sine Starts at $65/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 Sine includes Vizitor, Visitdesk, Envoy Visitors, Veris, VisitUs, TDS Visitor, Vizmo, SeQure Visitor Management Software and VizMan.