Comment by stcredzero

It could be argued that garbage collection, polymorphism, lambdas, and REPLs were semi-mainstreamed by Smalltalk. That's not to say that it was the first appearance of those features. However, it was a big incursion into mainstream awareness. In 2019, all of those things are squarely mainstream. In the 1990's, lots of programmers regarded them akin to "woo."