I have hundreds of ideas which I think can generate revenue of the sort you describe, but they need significant work each (execution). Note that $20k annually is already full annual salary in half of the world too.
A very simple one: interview scheduling tool integrated with multiple calendars.
Eg. when interviewing, sometimes I have a pool of interviewers, and I want a pair to be offered to a candidate (they only see time slots, obviously) with certain internal conditions (one expert from this pool, another from this pool; eg. tech stack or timezone), while equally loading all of them.
Sounds simple but I could never find a tool that does it, and I believe companies might be interested just like they get tools like calendly just for limited purposes.
iCal format is simple on the face of it, but companies have restrictions on the feeds, and accounting for recurring events and working hours is not as trivial.
