Many people have mentioned Monica, which is what I use for this.

I live overseas from loved ones and old friends, meaning there are few natural cues to encourage communication. Without very regular chats my memory doesn't let me be as in context with the major things happening in their lives as I need to be to have meaningful conversations with them. Monica helps with both of these things.

Getting reminders only really helps if the interactions themselves are also rewarding when you do them. If, say, calling an elderly family member feels more like a chore, it's easy to end up skipping the reminders more than you'd like.