Acuity Scheduling supports 2-way syncing with iCloud, Office 365, Outlook.com, Exchange and Google Calendar on all paid plans.
2-way syncing adds appointments in Acuity Scheduling to your calendar and optionally blocks off time in Acuity from events on your calendar. To get connected, head to Business Settings > Sync with Other Calendars and select the calendar you're using.
You can also set up a 1-way subscription with iCal/Outlook by clicking "Subscribe to Acuity..." under Business Settings > Sync with Other Calendars within Acuity. With that appointments added to Acuity will automatically show up in iCal/Outlook.