[chasil]

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

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

[madars]

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)

[wahern]

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