Moom

Moom's trick is that you do not have to learn anything first. Hover the green zoom button in any title bar and a small grid appears; click a cell and the window lands there. That makes it the one app in this category you can hand to someone who has no interest in keyboard shortcuts, while a full keyboard mode sits underneath for people who do want them.

The part you are really paying for is layouts. Name an arrangement of windows, then bring it back on demand or let Moom restore it automatically when a particular monitor is attached. It solves the same docking problem as Rectangle Pro, from a two-person shop that has been selling this app since 2010 — which is about as good a signal as you get that it will still be here in five years.

Read the licence wording before you buy, because it is time-based rather than version-based: $15 includes at least a year of updates and the licence never expires, but the move from Moom 3 to Moom 4 cost existing owners $8. Budget for something like that every few years if you want to stay current.

One buying trap worth repeating: the Mac App Store listing is Moom Classic, the older app. Moom 4 is a direct download. And if a shortcut for "left half" is genuinely all you need, free Rectangle covers it.