Move and resize floating windows using other windows and the edge of the screen as guidelines.

You can use this module with the following in your xmonad.hs:

   import XMonad.Actions.FloatSnap

Then add appropriate key bindings, for example:

       , ((modm,               xK_Left),  withFocused $ snapMove L Nothing)
       , ((modm,               xK_Right), withFocused $ snapMove R Nothing)
       , ((modm,               xK_Up),    withFocused $ snapMove U Nothing)
       , ((modm,               xK_Down),  withFocused $ snapMove D Nothing)
       , ((modm .|. shiftMask, xK_Left),  withFocused $ snapShrink R Nothing)
       , ((modm .|. shiftMask, xK_Right), withFocused $ snapGrow R Nothing)
       , ((modm .|. shiftMask, xK_Up),    withFocused $ snapShrink D Nothing)
       , ((modm .|. shiftMask, xK_Down),  withFocused $ snapGrow D Nothing)

For detailed instructions on editing your key bindings, see the tutorial.

And possibly add appropriate mouse bindings, for example:

       , ((modm,               button1), (\w -> focus w >> mouseMoveWindow w >> ifClick (snapMagicMove (Just 50) (Just 50) w)))
       , ((modm .|. shiftMask, button1), (\w -> focus w >> mouseMoveWindow w >> ifClick (snapMagicResize [L,R,U,D] (Just 50) (Just 50) w)))
       , ((modm,               button3), (\w -> focus w >> mouseResizeWindow w >> ifClick (snapMagicResize [R,D] (Just 50) (Just 50) w)))

For detailed instructions on editing your mouse bindings, see XMonad.Doc.Extending.

Using these mouse bindings, it will not snap while moving, but allow you to click the window once after it has been moved or resized to snap it into place. Note that the order in which the commands are applied in the mouse bindings are important. Snapping can also be used together with other window resizing functions, such as those from XMonad.Actions.FlexibleResize

An alternative set of mouse bindings that will always snap after the drag is:

       , ((modm,               button1), (\w -> focus w >> mouseMoveWindow w >> afterDrag (snapMagicMove (Just 50) (Just 50) w)))
       , ((modm .|. shiftMask, button1), (\w -> focus w >> mouseMoveWindow w >> afterDrag (snapMagicResize [L,R,U,D] (Just 50) (Just 50) w)))
       , ((modm,               button3), (\w -> focus w >> mouseResizeWindow w >> afterDrag (snapMagicResize [R,D] (Just 50) (Just 50) w)))

Interesting values for the distance to look for window in the orthogonal axis are Nothing (to snap against every window), Just 0 (to only snap against windows that we should collide with geometrically while moving) and Just 1 (to also snap against windows we brush against).

For snapMagicMove, snapMagicResize and snapMagicMouseResize, try instead setting it to the same as the maximum snapping distance.

When a value is specified it can be geometrically conceived as adding a border with the specified width around the window and then checking which windows it should collide with.