For workflow purposes, I still use a 2003 eMac running Leopard a decent amount of time, and really miss some of its features in the newer, less civilized downgrades of the operating system. In particular, the scroll bars by the side of the window (which one can force the OS to display, albeit far smaller than they used to be) used to have arrow icons to move up on down one screen. If one were really determined, this preferences setting allowed the arrows to appear both above and below the scroll bar.
In the newer OS versions that newer hardware is stuck with (say, anything that doesn't have a large cat name), is there any way (preferences setting, AppleScript, helper app, etc) to bring back the arrow icons to scroll up and down precisely one screen per click or, failing that, to bring back their functionality easily from the mouse/trackpad? Page Up/Down isn't really a solution, as it takes both hands.