The killer app is ChatGPT. I'm not sure what you're expecting here, but it's been enormously useful while trying out new languages. For example, even if it's not 100% right, it has been a great help while working with nix, as I'm often ignorant to entire methods of solving a problem, and it's pretty good at suggesting the right method.

It's also super useful for things like "convert this fish shell snippet to bash" or "rewrite this Python class as a single function". It tends to really nail these sorts of grounded questions, and it legitimately saves me time.