People say TeX doesn't have good tooling but I can't think of any other language where I can seamlessly intermix circuit diagrams with equations and plots. It's really nice to be able to draw on an axis coordinate system (pgfplots with TikZ), as an example.

The language itself is horrible and the skill floor is too high but the Turing completeness enables a ton of wacky features that would never be allowed in something like Mathematica.