I often feel like my primary language, c++, is somewhere between niche and mainstream.

It leaves ample opportunities to do something in a niche way. I am often disenchanted after reading many open-source, ostensibly high-quality c++ libraries — namely Apple’s WebKit and a few parts of Google’s Filament. That said, there are a few gems of c++ that I can’t describe as anything but archetypally niche.

Nlohhman’s JSON library (also, the constexpr fork of that library), and the CTRE library for compile time regular expressions are absolute gems.