Bulma is a free, open source CSS framework based on Flexbox and built with Sass. It's 100% responsive, fully modular, and available for free.

It's 2016, I don't believe developers should care about IE anymore as much as they shouldn't care about someone accessing their website using Nokia 7650, just detect if its IE, show a message to the user, and ask him to do himself a favour and switch to Chrome or Firefox

Saw it on reddit a few days ago. It's an interesting take on CSS framework because it tackles a lot of the current layout trend. There's only one thing that refrains me from installing it right now : The absolute absence of responsive features (is-visible is-hidden, layout push and pull for grid items...). Without those, it's barely a "responsive" framework in my opinion. Great project nonetheless, I hope to use it someday when it's a bit more mature!

Now we just need a Sketch file.