Responsive Design

I'm totally with you there on wanting to do everything by yourself, not being bloated with more css than what you're actually using.

But for little placeholder websites, bootstrap is great.
I'm wanting to work on a CSS framework for myself (and others, of course) that is super basic stuff that builds off of the html instead of classes, but don't get me wrong, there will definitely be classes because there is always a need for classes.

I actually did something like that. Many of my recent projects used a tile-based layout and I created a minimal-framework for that ^^

It just organizes tiles and makes them responsive.

Metro tiles are always fun to play with. :)