Java – replacing COBOL as the enterprise programming language; it is far, far ahead of all other languages in terms of popularity and job demand
Python – how did this relatively slow scripting language manage to become so popular for numerical computing, machine learning, data science, IoT, web development?
Lisp/Scheme – a homoiconic wonder with superb macro extensibility
Honourable mentions go to:
C – it underpins the entire IT industry (which includes Linux)
Forth – how can such a ridiculously simple language be so capable?
Emacs and vim – the “great” programming editors
OOP (object-oriented programming) – this programming paradigm has ruled the IT industry for more than three decades and shows no sign of loosening its grip, not even in the face of FP