You're still using (mostly the same) plain old LaTeX 2e with pdftex, xetex, and luatex (pdflatex, xelatex, and lualatex). Those are just 3 different engines for Knuth's original tex. As far as I know, some parts of all 3 are written in WEB (which is a language that persists mostly because Knuth's TeX is written in it).
You're still using (mostly the same) plain old LaTeX 2e with pdftex, xetex, and luatex (pdflatex, xelatex, and lualatex). Those are just 3 different engines for Knuth's original tex. As far as I know, some parts of all 3 are written in WEB (which is a language that persists mostly because Knuth's TeX is written in it).