MacOS – Maximise to half screen and choose other window

One of the easiest ways to do this is to use BetterTouchTool. It will let you bind a keyboard shortcut or a trackpad shortcut to many commands, including maximize window.

Once you are in the BTT settings page, do the following:

1. Go to the Keyboard tab on top.
2. On the bottom near Keyboard shortcut, enter in whichever keyboard shortcut you want.
3. For Predefined action, choose Maximize Window.

There are many other options related to maximizing besides "Maximize Window":

• Maximize Window Left
• Maximize Window Right
• Maximize Window To Bottom Half
• Maximize Window To Top Half
• Maximize To Next Monitor

I don't know any way to get the second frontmost application or window with AppleScript, apart from something like this:

delay 0.3 -- time to release modifier keys if the script is run with a shortcut
tell application "System Events"
    set p to process 1 where it is frontmost
    set visible of p to false
    delay 0.01
    key code 121 -- 121 = page down, 116 = page up
    set frontmost of p to true
end tell

It makes the hidden and activated windows flash though.

With browsers you could use window.scrollBy():

tell application "Safari" to tell document 1
    do JavaScript "window.scrollBy(0,(window.innerHeight-20))"
end tell

tell application "Google Chrome" to tell active tab of window 1
    execute javascript "window.scrollBy(0,(window.innerHeight-20))"
end tell

Another option would be to simulate pressing ⌃F4, page up or page down, and ⌃⇧F4 by for example using KeyRemap4MacBook:

<autogen>__KeyToKey__ KeyCode::CURSOR_UP, ModifierFlag::FN | ModifierFlag::CONTROL_L | ModifierFlag::NONE, KeyCode::F4, ModifierFlag::CONTROL_L, KeyCode::PAGEUP, KeyCode::F4, ModifierFlag::CONTROL_L | ModifierFlag::SHIFT_L</autogen>
<autogen>__KeyToKey__ KeyCode::CURSOR_DOWN, ModifierFlag::FN | ModifierFlag::CONTROL_L | ModifierFlag::NONE, KeyCode::F4, ModifierFlag::CONTROL_L, KeyCode::PAGEDOWN, KeyCode::F4, ModifierFlag::CONTROL_L | ModifierFlag::SHIFT_L</autogen>

It also causes a visual glitch, and ⌃F4 sometimes selects windows from hidden applications.