I do carpet cleaning on weekends as a side hustle, and most of my clients return about every six months. I still keep track of all my clients in a notebook, which works as long as I don't forget to contact someone.
I'm trying to find something simple that would allow me to keep track of client notes, set reminders for re-cleaning, and maybe send short text messages when the next cleaning is due. I don't need dispatching, route planning, or a lot of features for the entire team since I work alone.