I think Alan Kay's OOP is widely used, but not at the "program" level. From what I understand, according to Alan Kay, OOP is about message passing, late binding

I think Alan Kay's OOP is widely used, but not at the "program" level. From what I understand, according to Alan Kay, OOP is about message passing, late binding and internal state. This is the way lots of software works these days with JSON over HTTP, or protocol buffers, or something else. I think at some point people imagined that there would be a point where you could buy or use objects from other people to build your programs more efficiently. I think that's what happened, with some companies offering very specific objects (auth for example, or persistance), while other offer a library with everything you need (cloud providers). And we even "rediscovered" the concept of interface in a way with stuff like "compatible with the S3 API".