Windows only: Feel the Wheel does just two things, but does them very well with a minuscule application size. The utility, sometimes called Feewhee, resizes windows and adjusts their transparency using your mouse wheel.
Feewhee is a tiny, no-footprint utility that uses 900KB of memory when running, and it runs fairly smooth, too. Hover your cursor over a window title bar, then scroll up or down. The window resizes as you scroll, though if it sizes past where your cursor is, you'll need to move back — it seems like you'd quickly train yourself to grab windows toward the left side, though. If you hold down Shift while scrolling, the window becomes more transparent or opaque.
That's all Feel the Wheel/Feewhee does, but that's pretty handy for anyone who needs smaller windows or occasional transparency. It's a free download for Windows systems only.
Feel the Wheel [Nattyware]