The way that applications, windows and our OS behave is a subject of much debate. Toss some life-long switchers into the mix and boy-howdy, you got yourself the nerd version of a bar fight. One of these much debated behaviors between Mac OS X and Windows is how to handle switching between applications and their windows. Mac OS X focuses on applications - when you press cmd + tab, you can switch between all of your open applications, but you have to press cmd + ` in each app to cycle between the windows specific to said app. The Windows switcher, on the other hand, doesn't see applications, only windows. Pressing the switching keystroke equivalent of alt + tab offers a selection of all open windows, including the 20 Word documents and 5 IE sessions you have running.
For the sake of this post, I'm not necessarily saying one is better than the other, and the subject of why this difference exists is a usability discussion best left for another day. I simply wanted to lay some context for Witch, a Windows-like application switcher from Peter Maurer (of Butler and the original Textpander/TextExpander fame) that fuses window-centric switching with some of the nice perks of Mac OS X. Not only can you switch between windows, just like on, uh, Windows, but you can also do things like bringing all minimized windows to the front or even close those minimized windows without having to bring them to the front.
Witch, like many of Peter's apps, is donationware. However, if you get attached to it and don't want it to go the way of TextExpander (or if you simply want to give a developer his much-due credit), I highly recommend you donate for Peter's fine work.