I've got a few full old backups of things like binary database dumps. Obviously, they don't differ much so doing full backups is not the smartest idea here. For now, I'm looking for a compression program capable of taking an advantage from the fact, that most of the files have a similar content.
If you first tar the files (using
tar cvf my_backup.tar <file list...>) then any compression tool will do a good job as they will see the data as one big file.
So just tar the files, and then put them in a zip, 7-zip, bzip2, etc. From the tar file, you can try the different compression algorithm and see which one performs best.
I've had very good luck with 7-Zip. If you have the horsepower, it is capable of operating with a very large window. Make sure your original files are as uncompressed as possible so it can find similarities. (For Excel files in a heterogeneous environment, for example, this means unzipping their contents first, since xlsx files are lightly compressed when they're stored. I was once able to compress 600 MiB+ of almost-redundant Excel version files down to a few hundred KiB.)