Ask HN: What re-engagement technology exist out there?

Hey, fellow hackers!

I’m looking for different solutions to reengage the users of my web/mobile/desktop apps. My research shows that re-engagement involves a lot of advertisements (of which I am not a particular fan of), and things like deep links, push notifications, and email marketing re-engagement campaigns.

Is there something else? Something like SaaS that I can integrate into my applications and have the re-engagement happen on auto-pilot or with much smaller effort?

What tech/tooling exists today?

Are there any start-ups on the horizon seeking to disrupt this space?