It's good to see something else than Bootstrap. If you like this, have a look at: http://www.semantic-ui.com/ - I love using this as every component can be downloaded separately.
I find Semantic UI to be very very interesting, but I have yet to figure out how to integrate it in my projects. I don't know if it's just me but it feels like they are forcing you to write your own styling in a separate repo, then generate the CSS and use it on your project, which to me, makes no sense.
I tried to use Semantic UI and I didn't grasp it properly. Don't get it as negative criticism but I found there is a simple tutorial and its grid is kind of unusable even looking examples.
In my last project ended using Zurb Foundation although I had Semantic UI as first option. Any pointer will be useful.
I also use semantic-ui and can only say good things about it expect for those situation where I search for a particular "widget" such as a split button and cannot quickly find good results.
Inuit https://github.com/csswizardry/inuit.css uses BEM and the most pedantically correct CSS framework out there. It is a bit more work to get into it as it doesn't provide design off the go--you'll have to add colours, shadows, bevels or whatever else you want. However, that's probably a good thing as it forces you to assimilate the architecture which is a transferrable skill.
I probably missed something.