I gravitate towards Bootstrap for most of my projects as it's so darn easy to whip up something that looks decent in a short amount of time, but on the flipside I'm starting to feel that if I have to look at another Bootstrap site my eyes are going to start bleeding.
I found, and like, Project Clarity[0] from VMWare, however it's mostly focused on an Angular use-case whereas I would like something more JS framework-agnostic.
[0] https://clarity.design/