Appointy has been around for a very long time, Archive.org suggests 2011 was the starting year for the service. Appointy has been redesigned and rethought several times with an attempt to improve the UI and UX. In truth, they have made progress. The Appointy UI is clean upon first inspection and relatively intuitive. However, once you dive in there are a ton of complex, confusing settings and sub settings and huge sub menus and addons. Basically it is not easy to use. I think a layman user could get away with a simple setup, and a more advanced user could (likely with the help of support) attain comfort with the UI, but it is most certainly a beast.
Appointy does try and tow the line between being a marketing tool, a ticketing tool, a payment tool and a scheduling tool. None of these things are accomplished beautifully.