Dudle - Dudle is an online scheduling application, which is free and open source.
Acuity Scheduling - Automate your client bookings, cancellations, reminders & payments using the worlds friendliest online scheduling software.
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.
Framadate - Make your polls
MINDBODY - Find and book fitness and beauty classes near you.