Calendly solves one problem well: letting someone pick a free slot on your calendar. For a therapy practice, that is the first step in a longer chain — intake and consent, the session itself, notes afterward, and getting paid — and Calendly has no opinion on any of the rest of that chain.
Instead of Calendly for booking, Zoom for the session, a forms tool for intake, and a separate invoicing app for payment, Trance OS keeps booking, GDPR-compliant intake, a native clinical video room, client records, and Stripe-based payments in one system tied to the same client record.