Menu: Adjust - Polar Coordinates
Converts Rectangular Image to Polar and vice versa. Similar to the Little Planet (Stereographic projection).
This has most usage for making Light Probes but it is also effective for various effects.
If the image is not a natural 360 panorama you can blend the edges with the Blend dial - either mirroring the blend or overlapping it.
Follow frame is a special Rectangular to Polar coordinates where the result is formatted into a rectangle rather than circle.
Tip: It can be also used with various seamless graphics to create unexpected circular patterns.