Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
BookSteam - BookSteam Online booking and appointment scheduling software for businesses worldwide. Easy to use, cloud based web scheduler that includes class and group bookings. Calendar management and schedule organization, trusted by thousands.
Slack - A messaging app for teams who see through the Earth!
MINDBODY - Find and book fitness and beauty classes near you.