There isn't much competition here, Hugin is currently the most sophisticated and easy to use tool for stitching photos and assembling panoramas on Unix/Linux systems (also available for Windows and OS X).
There are some optional tools that can be used in conjunction with hugin, but none of these are actually required to produce high quality results:
- autopano-sift - Save time by automatically generating control-point pairs, requires the mono .NET runtime.
- autopano - Similar to autopano-sift (Freeware).
- enblend - Perform sophisticated blending of seams when overlapping photos have varying brightness.
- PTStitcher - Freeware alternative to nona, the internal hugin stitcher.
- PTmender - Open Source replacement for PTStitcher, part of the pano12 package.
Linux tools overview
For a full list of Unix/Linux tools, see the Linux category page.
Useful helper tools
- ImageMagick: Optionally batch process images before using Enblend, e.g. when you have large black areas because of a pitch angle.
Plugins for the Gimp
The Gimp is a sophisticated image editor.
There are several panoramic photography related gimp plugins that can be used to manipulate panoramas.