CUR
ICO's cursor-shaped cousin.
Where it came from
CUR is the cursor sibling of ICO, also from early Windows. It stores the same multi-resolution bitmaps but adds one field ICO lacks: the "hot spot" — the exact pixel that counts as the click point.
You meet CUR in .cur files used for custom mouse pointers on the web and in Windows themes. Functionally it is ICO with a pointer.
How it works
Like ICO, CUR is a container of small images; the extra hot-spot coordinates (x,y) tell the OS where the arrow "tip" is. Without it, every cursor would click from its top-left corner.
UWC converts CUR → PNG/JPEG server-side, flattening the frames into a usable raster.