Windows: AquaSnap is a free multifunctional tweaking application that brings Aero-style effects to Windows XP and enhances Aero in Vista and Windows 7.
If all you're interested in is taking advantage of Aero-style effects in Windows XP like snapping application windows to the edges of your monitor, AquaSnap has you covered. You can step beyond the basics in XP, Vista and Windows 7 with additional AquaSnap tweaks.
You can set applications windows to become semi-transparent when moving or when shook, as well as specify whether you want to have windows snap like true Aero windows or snap with AquaSnap's custom snapping that enables all edges of the monitor.
AquaSnap is freeware and works with Windows XP through Windows 7. Have a favourite application for tweaking the Windows user interface? Let's hear about it in the comments.