The Quality Without A Name is Christopher Alexander's term for an attractive feature which is not quite "beauty" or "comfort" or "aliveness" or any other term. But which we can recognise in buildings.
For those influenced most by Alexander's pattern-language thinking, we probably think we can see it in software too : either for end users or in the form of software architecture or a well designed API.
So what are your favourite examples of QWAN and why?
If we are talking about design, then the ability to tweak, expand or redefine the original behaviour with minimal changes would be something that I find appealing. Some, however, would claim that this quality attribute has a name: maintainability.
Still, from a pure abstract perspective of software architecture, I would say that the ability to easily invoke in your mind an isomorphism between the concrete architecture and the intended domain/purpose, is a quality without name.
Smalltalk. So much of what you need in a programming language in so little constructs