libungif is a library for reading and writing GIF files. The 4.1.3 Release is a cleanup of bugs in the Extension Handling Code. In particular, if you had issues when using multiple subblocks for an Extension or longer than normal comments, this release should fix it.
libungif is able to read and manipulate all GIF files. However, it only writes uncompressed GIFs which do not use the LZW algorithm patented by UniSys. Although this patent has expired in the United States, patent searches by the FSF show that worldwide patents exist until 2006. By not including LZW compression libungif is freely redistributable throughout the world.
That said, 4.1.3 of giflib, a GIF manipulating library that supports LZW compression is being released concurrently with this release of libungif. If you live in a country where the UniSys patent has expired you may consider using that instead. Please get giflib from the sourceforge site where you found libungif.
If you are using libungif on MS Windows, you may be interested in the code in the windows subdirectory provided by Lennie Araki under the same terms as the libungif library. Unfortunately, I do not have a Windows environment to maintain this code. If anyone wants to keep it functional, patches and developers are welcome.