Below are simple styles to "flatten" bootstrap. I didn't go through every control and widget that bootstrap offers, only what was required for https://commando.io, so your milage may vary.

bootstrap.flatten.css

/* Flatten das boostrap */
.well, .navbar-inner, .popover, .btn, .tooltip, input, select, textarea, pre, .progress, .modal, .add-on, .alert, .table-bordered, .nav>.active>a, .dropdown-menu, .tooltip-inner, .badge, .label, .img-polaroid {
 	-moz-box-shadow: none !important;
	-webkit-box-shadow: none !important;
	box-shadow: none !important;
	-webkit-border-radius: 0px !important;
	-moz-border-radius: 0px !important;
	border-radius: 0px !important;
	border-collapse: collapse !important;
	background-image: none !important;
}

Manage servers easily online.

https://commando.io

nice!

Or, just use https://github.com/littlesparkvt/flatstrap

@bevacqua - I dunno. I think i would prefer this way over Flatstrap. It allows you to use the official bootstrap repo with a minimal 10 line addition as opposed to waiting on yet another third-party to always be catching up to Bootstap's updates.

@bevacqua - Flatstrap looks really appealing on the surface, but its implementation is actually a little frightening. To make Bootstrap flat, they literally rewrote the relevant mixins:

#gradient {
    .horizontal(@startColor: #555, @endColor: #333) {
        background-color: @endColor;
    }

    etc...

I find this approach really frustrating if your "flat" design actually does call for a gradient or two.

Don't forget about all the filter tags for IE compatibility.

or use
http://designmodo.github.io/Flat-UI/
http://purecss.io/

I wonder if it would break anything serious to just go all the way and slap that sucker on the body tag...