
A tool for visualizing what the Align Rotation to Vector geometry node is doing (or Align Euler to Vector in 4.1.1 and earlier). This tool is featured in an upcoming video that's coming soon!
The tool shows a visual representation of the rotation output that the node calculates given a vector input. Basically, what's happening is the node calculates the Euler rotation between whatever vector you input and the X, Y or Z axis.
There are some other inputs, but the only two that I've used are the X,Y,Z selection at the top and the vector input itself. The tool isn't really designed to worry about the "Pivot" or "Factor" inputs which can be useful but are limited to edge cases. "Pivot" limits the rotation to a specific axis and "Factor" determines how much influence the input vector has on the output rotation.

The animation switch will turn on axis-by-axis animation of the rotation that helps to show the sequence of rotation, how it affects a vector and the end result of that rotation. You can adjust the playback speed but note that there may be some jumping around as you adjust since the playback is on a short loop and will restart.

There are two ways to input a vector. You can manually choose a vector (note that your input vector will automatically be normalized) or use the cursor to aim a vector wherever you choose (you'll need to click on the cursor after enabling "Pick Vector With Point" in the settings panel).
The other settings enable or disable visualization features so play around with those and enjoy the tool! As always, let me know if you have any questions or bug reports via email: inquiries.malcolm@gmail.com