You can export a copy of your Gazelle Data at any time. Just go to https://gazelleapp.io/app/settings/exports or go to Settings → and scroll all the way to the bottom left hand corner to hit "Export Data"
Select the Data Tables you want to Export. All clients, pianos, events, invoices, and reminders will be linked by a common Client ID number so you can associate things outside of Gazelle.
If you are wanting to export a specific calendar to an outside calendar program (Google calendar, phone calendar app, etc) go HERE to view the steps.