ShadowSweeper

ShadowSweeper brings a simple, clean, flat look to your desktop by disabling shadows under windows and menus.

Those shadows can bring dimension, depth, and richness to your display, but they can be a problem, especially when you wish to place two windows side by side seamlessly, with no overlap.
Just launch ShadowSweeper to disable shadows, and launch it again to bring them back. Other approaches have used system hacks, which can de-stabilize your system. ShadowSweeper does not use system hacks, so it does not impact system stability.
Known limitations: The shadow under the menu bar is still present.
See ShadowSweeper in action: https://vimeo.com/71726756.