Is there a window tiling app that snaps to other windows' edges rather than predefined screen areas? All window tiling apps I've seen are designed to make windows snap to preset screen areas, such as "the left half of the screen" or even "this size of rectangle specified with a grid." Is there one that would let me do, say, this:
Take a look at this Wiki question, and see if any of the answers meet your needs.

In particular, this one looks interesting:

Zooom/2 - "Magnetism. If you like snapping windows the the edges of the screen or other windows (as in many X window managers), you will love this."