A previous discussion on Capiche about Segment alternatives had mentioned Hull and Freshpaint as being alternatives. Of those, Freshpaint looks more like the standard Segment alternative for directly connecting applications, where Hull is building customer profiles in what might be closer to Segment Personals—and it connects to Redshift and Salesforce among others. Could be worth checking out.

I'd second checking out Hull.io on the cheaper side or Lytics on the pricier side.

I'm looking for something similar myself.

Checkout windsor.io and see if it works for you.

Are you looking for a source of truth for internal use, or external ad audiences?

For internal analysis/source-of-truth for your customers, if you're using Segment's base plan (or MetaRouter or Rudder Stack etc.), some of their destinations will allow you to aggregate behavior. For instance, in Amplitude, customer look-up allows us to keep track of actions performed within our product, but also within our mailing platform (Customer.io).

On the database front: In addition to sending that information to Amplitude, it all lives in Redshift, making it easy to do joins etc. Combine that with something like DBT for transforms and you might be able to get user actions transformed in a uniform place.