PowerSchedule is a registraiton tool that allows you to manage everything related to the event - registraitons, resources, event setup, etc. - inside of Dynamics 365. However, with PowerSchedule, attendees cannot register themselves, and does not have the built-in functionality to allow you to charge money for an event. PowerZapEvent is also managed 100% inside of Dynamics 365, but is actually an integration between Dynamics 365 and the third-party event management tool, ZapEvent. PowerZapEvent doesn't have the concept of managing resources built into the add-on, but it does give you the ability to have registrants register online, and collect payments for those registrations.