Ask HN: What are some niche features of your go-to programming language?

After a decade of professional software dev, I've come to realize the importance of choosing the right language for each project (when possible).

For example, I work in C#/.NET if my customer primarily uses Windows. For legacy systems customers I do work in Java. When I'm working in prototypes I'm using Python.

For instance, recently I found Python with Numpy to be incredibly easy API wise to do some least squares computations on some datasets.

I wanted to know what are some intriguing niche features like syntax, libraries or tools that your go-to programming language excels at when compared to others?

My intention with this post is to have some kind of index that if your solving a specific problem one should consider a specific language. Not to ignite language wars etc.