Neither Planstack nor Calendar offers a free trial.
Planstack is designed for Medium Business and Small Business.
Calendar is designed for Individuals, Large Enterprises, Medium Business and Small Business.
Pricing for Planstack Starts at $10/User whereas for Calendar Starts at $6/Month when Billed Yearly.
Some top alternatives to Planstack includes Posted, EasyContent, Cal.com, Calendar, neatCal, CalendarX, Qualified, Workvivo, CalendarWiz, Nous, Exly and IFTTT.
Some top alternatives to Calendar includes Appointy, Calendly, Cogsworth, Scedule, OpusTime, Book Like A Boss, Calendar.AI, EasyCalendar, Hupport, Office Tracker, Schedule it, Schedule.cc by 500apps and DaySchedule.