Love the tidycal for booking clients. Simple interface, flexible features. With few more enhancements this will be quite powerful calendar tool. Few things I love
1. Manual Approval.
2. Send notification to team members. More like FYI.
3. Teams and agency options.
4. Multiple bookings, this allows clients to pick different days but not two different slots on same day.

Features that will enhance
1. Remove tidycal logo for paid users.
2. Have option to select multiple durations ( zcal has this).
3. Custom domain.