LLMs
Emacs
GitHub Copilot
It's pretty amazing. Great for boilerplate code, and a great autocomplete. Makes writing tests and writing code faster.
It also changes the way I write code: I first write a descriptive plain-english comment, and if I'm descriptive enough copilot can almost always get the next line right.
On a few rarer occasions, I've used the copilot chat to help get un-stuck in difficult problems, mostly as a brainstorming buddy.