WISC - Widefield Star Calibrator

S + click selects an image star; then click the matching red catalogue star. You might need to scan around a bit to find the star you are looking for.

Wheel zooms and drag pans the image. Hold Cmd/Ctrl while using the wheel or dragging to adjust the lens model. On a Mac trackpad, hold ⌘ + Shift before a normal click-and-drag left/right to rotate the lens; no right-click needed.

X toggles between the star catalogue view and the image, which is useful while checking a match.