UNO is a theme that brings the sunken unified toolbar/titlebar look&feel to every single window on your system (metal or aqua, and already unified windows as well).

Source: gui.interacto.net - The Sunken Unified GUI for Mac OS X 10.4.x (Tiger)

I ran the UNO installer on my PowerBook a few weeks ago, hoping to smooth out the scourge of inconsistent UI themes that have accreted around OS X. And pretty much, that's what it's done.

In fact, that installer went so far as to tweak my Firefox UI by replacing my userChrome.css, which I just realized as I was poking around in it to make my Tab Sidebar smaller.

On one hand, I really appreciate the thoroughness. But on the other, I had a few tweaks of my own in there that this thing blew away. I wish they'd appended to and not replaced this file.