a while back I read about someone using such a system to stay in touch with contacts in their professional network. I forget the particulars, but basically he bucketed people he wanted to stay in touch with into (I think) weekly, monthly, quarterly buckets with max numbers of people per bucket and reached out to them at those respective intervals as a spreadsheet.

I think a mix of calendar, multi-channel communication monitoring system to keep track of people I keep in touch with packaged into a "daily task list" interface would be highly valuable for making sure I don't forget to keep in touch with important people in my network.