Free data compression software for linux

Ext2 compression extension (E2compr) is a small patch against the ext2 filesystem that allows on-the-fly compression and decompression. It compresses only regular files; the administrative data (superblock, inodes, directory files etc.) are not compressed (mainly for safety reasons).
Access to compressed blocks is provided for read and write operations. The compression algorithm and cluster size (see section Clusters) is specified on a per-file basis. Directories can also be marked for compression, in which case every newly created file in the directory will be automatically compressed with the same cluster size and the same algorithm that was specified for the directory.
E2compr is not a new filesystem. It is only a patch to the ext2 filesystem made to support the EXT2_COMPR_FL flag. It does not require you to make a new partition, and will continue to read or write existing ext2 filesystems. You should consider it is only a way for the read and write routines to access files that could have been created by a simple utility similar to gzip or compress. Compressed and uncompressed files will coexist nicely on your ext2 partitions.
Usage
Basically, a file is compressed with the command `chattr +c filename, and decompressed with the command `chattr -c filename. You can also do `chattr +c (etc.) on a directory. The directory itself wont be compressed, but any new files created in that directory inherit that directorys compress flag and compression algorithm and cluster size.(1)
Use lsattr to see if a file should be compressed or not, and to see what compression algorithm and cluster size will be used.
Use e2ratio to see how much disk space is used by the compressed form compared to the uncompressed form.
You can also try the `-u or `-r options to lsattr. (The difference is that, for directories, e2ratio finds the disk usage of the whole directory tree, like du, whereas `lsattr -u only shows the space taken by the directory file, like `ls -s.)
Enhancements:
- kernel 2.4.26 and 2.6.18.5 patch sets.
- Allows repeated compress/decompress cycles.
- The ability to compile within a compressed directory tree.
- This release corrects small file sizes and fixes all known GPFs.
- It removes compiler warning messages and regularizes debug output.

RPM Delta Compression Virtual Update Repository is an experiment to explore the possibility of significantly reducing the bandwidth required to apply updates to a Fedora installation.
This software includes a server which provides a virtual update repository to clients such as yum, up2date, or other update tools. RPM Delta Compression Virtual Update Repository also includes a utility to create and maintain a RPM delta repository.
The server will attempt to generate the update RPM from a small delta file applied to a locally stored RPM from the original distribution.
Enhancements:
- This version utilizes the SuSE deltarpm tool as the underlying delta generator.
- It features both HTTP virtual update of the RPM repository (using Tomcat servlet container) and command line tools for generating update RPMs from a delta repository.

Data.FormValidators aim is to bring all the benefits of the perl module Data::FormValidator over to javascript, using the same input profiles (they can be dumped into javascript objects using the perl module Data::JavaScript.
Data.FormValidator library lets you define profiles which declare the required and optional fields and any constraints they might have.
The results are provided as an object which makes it easy to handle missing and invalid results, return error messages about which constraints failed, or process the resulting valid data.
IMPORTANT NOTE: JavaScript form validation is NOT a replacement for data validation in your backend scripts. This is the primary reason this module was written... so that it would be easy to share the same validation profile for both the frontend (via Data.FormValidator.js) and backend (via Data::FormValidator.pm).
Enhancements:
- A problem where some functions were not terminated by a semi-colon, so JavaScript compactors would end up creating broken code was fixed.