You can see all of the utilities this way. The ex editor is also standard.

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/

TIL: busybox has ed and vi but not ex. https://www.busybox.net/downloads/BusyBox.html (so ex might be nice to learn but it might be not available on common systems like OpenWRT)

Technically, vi and ex are part of the User Portability Utilities extension.