@coderanger @andrew I'm not sure what EMF is, but I'm guessing it's a planned event/festival. I'm usually on the EMS field response side of the house, but in the instances where we've had to stand up dispatch ourselves, and I've had say in the matter, I've used Resgrid. They have extremely reasonable monthly plans, and an API! They're also VFD's so give them all the support you can.
Otherwise, I've been forced into many of the same systems you've probably also experienced, from home grown to "Click here to contact sales" level pricing. They're never exactly what you want, or too much of what you don't want, and ultimately whatever works for you is what's best. I've handled 1M+ events with Apple Notes (https://ampledata.org/san_francisco_pride_2013.html ) , Post-Its, White Boards, and paper & pen.
Of course, there's always the tried and true shared Google Sheets!