Calendly

Calendly connects to Google, Outlook or iCloud calendars, checks for conflicts and shows only open times, in the visitor's own time zone. Event types set the length, buffers, questions to ask and the video link (Zoom, Google Meet or Microsoft Teams). A booking page can be embedded on a website inline, as a pop-up widget or as a pop-up text link, and on paid plans it can take payment through Stripe or PayPal before a meeting is confirmed.

The API works on every plan, for listing events and invitees or creating single-use booking links; webhooks that tell your server when someone books or cancels need a paid plan. Round-robin scheduling, lead routing and Salesforce sync sit in the Teams tier. Cal.com is an open-source alternative that can be self-hosted.