Ask HN: What's the name for an app which someone uses purely for utility?

What I mean is an app that becomes a fundamental part of a person's work ecosystem like Gmail, a CRM, or an admin dashboard for the back-end of a website.

I remember coming across something on HN a while back about how the principles of design are very different when an app is not about attracting and retaining new users, but making people who interact with the world through your app more efficient and powerful. More focus on things like keyboard shortcuts, automation, and speed rather than pure simplicity and ease of use.

Does anyone have any resources on this, or know what the name for this is? Google is failing me.