Let’s do contacts for this discussion thread.
I’m still in the Apple ecosystem, so I let the OSes (macOS, iOS, etc.) handle that. The sync is almost seamless, or rather, this is the best of all the devils. My personal and work are intertwined; thus, it is more of a tag-ish layer of friends, acquaintances, etc. Yes, sometimes I mix the joke of friend Archetype-A with friend Archetype-B and vice versa. ;-)
Last time I checked, my Contacts had almost 5,000 entries in there and I don’t mind this part growing. I’ve tried Dex[1] for about a year+ but found it slow. Their work seems to have slowed and stalled, while you expect them to “move beyond a tool that seems to be still in beta.” This was a few years ago, and hence I’ve no idea about their current situation.
I also tried Monica,[2] but she do not know how to keep things in sync. The developer/team also seems to be focussing on an office suite that has been “Coming Soon in 2002” since 2021.[3] If you want to try out Monica and see if this fits, I suggest spinning one quickly with PikaPods[4] for less than $2 a month.
Now, I’m trying out Clay[5] for broader outreach and staying in touch with people with whom I’ve interacted or connected via the networks that I was and am part of.
For the closer and final few inner layers of my Onion of Contacts, I use a simple spreadsheet inspired by Derek Sivers[6] and Jakob Greenfeld.[7] This is where I have the people with whom I can be in touch regularly (monthly, quarterly, half-yearly, and yearly). This is not very strict, and I tend to have these as recurring tasks in my calendar, along with my usual digital chores. The spreadsheet's contact list will ideally be between 20-100 at max. These are the ones I call/write/text regularly, wish/attend birthdays, parties, remember anecdotes, their family, etc.