For those in Australia you can try Activeamigo. It’s free to list with all features including online payments and booking system included. https://www.activeamigo.com.au/business
For anyone in Australia there’s Activeamigo. You can list your classes for free and cancel at anytime (no contracts). https://www.activeamigo.com.au/business
I recommend having a look at Timely (www.gettimely.com). Timely is great to manage the bookings for your classes and PT sessions. It automates you reminder process with SMS and emails reducing the number of no-shows. Although, it is not a complete solution for Gym management it is used by thousands of fitness professionals around the world.