For the absolute lightweight, there is vi, eMacs, nano, etc.
For a UI I’ve been using VSCode. It is quite quick when you disable all extensions and most settings.
vi and emacs are absolutely not lightweight, let alone "absolutely lightweight".
I'm sorry but you cannot use VS Code and lightweight in the same sentence.
> absolute lightweight
> eMacs
I love Emacs, but I don't see how a Lisp platform with a web browser, a Tetris implementation, and 4 terminal emulators (shell, term, ansi-term, eshell) can be considered 'lightweight'.