This is an ERD for a hypothetical investment robo-advising app, like Betterment's or Wealthfront's.
Of course, a robo-advising app is incredibly complex, so this ERD should only cover a small part of its functionality.
I built this ERD with draw.io. To extend or modify it, download the file and import it to draw.io.
To read more about this project, check out this post on my blog.