We used to use Foundation but then found it was so easy to misuse and it got to the point where we were only including the grid so i've made a very small base we start projects from.

We have a couple of grid mixins that handle "rows" and "columns" but no grid system.

We use px for everything as it's how most people think in then we use postcss to change some of our px values to rem.

We personally use ECSS (http://ecss.io) which isn't exactly BEM but it borrows some principles from it.