Shift scrolls sideways
Shift with a mouse wheel follows the mouse's left and right. With ⌃, ⌥ or ⌘ too it's a shortcut, and keeps up and down.
Two devices, two ways
Each its own way
Natural or Standard for the trackpad and for the mouse, up and down and left and right. They mean the same whatever System Settings says.
Or let it find out
Scroll a page the way you would, and Newel sets each device from which way your hand went. Scroll the other way to change it.
A Magic Mouse is a mouse
Newel knows which device sent each scroll, so a Magic Mouse scrolls like your mouse, not your trackpad, even with both in use at once.
Only the direction
No smoothing, no acceleration, no remapping. About 15 µs a scroll, and nothing running while you're not scrolling.
Private
It asks for Accessibility and nothing else, and keeps nothing it sees. Diagnostics have counts only, never an app's name or where the pointer was.
At home on your Mac
A native app, small and calm: system fonts and controls, a welcome that shows you around, and a menu bar icon that's the stair it's named for.