What are three things that is must in 1-1 calendar scheduling tool?

Today, calendar scheduling market is crowded with lot of tools like calendly, cal.com etc. with tons of feature and options with higher pricing. But for simple 1-1 scheduling, what are the features that needed for solo founders, professionals like indie hackers, developers, PMs, students, researchers for simple networking with prospects.

Is there any tool who provides minimal things?