https://cdbaby.com/

Makes sense.

Why not stand alone app?

Matrix and Simplex is fine but I would recommend Signal for family and friends. Threema is also option but not user friendly for friends and family who wants easy user discovery than sharing userIDs.

I am using https://play.google.com/store/apps/details?id=vopo.easyhomefinance

It was open source but can’t find source now

GrapheneOS