What software do you use for scheduling viewings?

With OpenRent not having a scheduling tool, what do you use?

I’ve come across one, Koalendar which looks good and simple but seems to lack functionality; no restriction on persons from multi-booking and not permitting quarter hour slots rather than half hour. The latter appears to be possible with the pro version but I’m not keen on giving my credit card details out willy-nilly straight off.

Others I’ve found seem overly complicated for my / our needs.

Any thoughts?

A good old fashioned diary!!