Are there free or better alternatives to Fisheye-Hemi for defishing fisheye photos?

Yes. Free alternatives mentioned include Fred’s defisheye script for ImageMagick and Fulla, the command-line tool included with Hugin. Another option is GIMP with the MathMap plugin, which can convert fisheye images into several projections such as rectilinear, stereographic, Mercator, or Lambert conformal conic depending on the look you want.

Compared with those, users report Fisheye-Hemi is often better for this specific task because it does not simply remap to a standard rectilinear projection. Its custom mapping tends to preserve more of the frame and edge sharpness while still straightening lines, whereas standard defishing can soften edges and require a heavier crop.

Also check whether your software already supports fisheye lens profiles. Lightroom profiles for some fisheye lenses can correct and remap images to projections like rectilinear, equal-area, equidistant, or stereographic, and a similar profile may work if an exact one is unavailable.

So: if you want free, try Hugin/Fulla, ImageMagick, or GIMP/MathMap; if you want results closest to Fisheye-Hemi’s look, Fisheye-Hemi may still be preferable.