Tool for comparing Jar files or Zip files.
Home page: http://activityworkshop.net/software/jarcomp/
If you have two jar files or two zip files, it will show you what the differences are in the contents. It shows which files have been added, which have been removed, and which are present in both archives. If a file is found in both, it will tell you whether the file has grown bigger or been reduced in size, or if it's the same size in both. If it's the same size, an md5 checksum can be made for both files to see whether they're really the same contents or just the same size.
It can be useful to compare different versions of the same archive, for example to check that no files were accidentally added or forgotten, and that all the changes to the files are the ones intended.