zlib is designed to be a free, general-purpose, legally unencumbered, lossless data-compression library for use on virtually any computer hardware and operating system. The zlib data format is itself portable across platforms. Unlike the LZW compression method used in Unix compress(1), the compression method currently used in zlib essentially never expands the data. (LZW can double or triple the file size in extreme cases.) zlib's memory footprint is also independent of the input data and can be reduced, if necessary, at some cost in compression.
rsync is a replacement for rcp (and scp) that has many more features. It uses the "rsync algorithm" which provides a very fast method for remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand.
Recovery Is Possible (RIP) is a CD or USB boot/rescue/backup/maintenance system. It has support for many filesystem types (Reiserfs, Btrfs, Ext2/3/4, HFS+, ISO-9660, Squashfs, UDF, XFS, JFS, UFS2, CIFS, MS DOS, NTFS, and VFAT) and contains several utilities for system recovery. It also has IDE/SCSI/SATA, RAID, LVM2, and Ethernet/Wireless network support.
pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info written by Photoshop 5.0 as well as the erroneous iCCP chunk written by Photoshop 5.5.
HTTrack is an easy-to-use offline browser utility. It allows you to download a Web site from the Internet to a local directory, building recursively all directories, getting HTML, images, and other files from the server to your computer. HTTrack arranges the original site's relative link-structure. Simply open a page of the mirrored Web site in your browser, and you can browse the site from link to link, as if you were viewing it online. HTTrack can also update an existing mirrored site, and resume interrupted downloads. WebHTTrack is a Web-based GUI for HTTrack.
Bacula is a set of programs that allow you to manage the backup, recovery, and verification of computer data across a network of different computers. It is based on a client/server architecture and is efficient and relatively easy to use, while offering many advanced storage management features that make it easy to find and recover lost or damaged files.
GNU xorriso creates, loads, manipulates, and writes ISO 9660 filesystem images with Rock Ridge extensions. Files can be copied in and out. The session results get written to optical media or to filesystem objects. Rather than needing external tools for ISO 9660 production and CD/DVD/BD burning, it is a static compilation of libburnia-project.org. Thus GNU xorriso depends only on fundamental operating system facilities.
UnZip will list, test, or extract files from a ZIP archive, commonly found on DOS and Windows systems. A companion program, Zip, creates ZIP archives; both are part of the Info-ZIP project. Both programs are compatible with archives created by PKWARE's PKZIP or Nico Mak's WinZip, but in many cases the program options or default behaviors differ.
libburnia is a project comprised of libraries and binaries for reading, mastering, and writing optical discs. It provides libburn, a CD/DVD/BD burn library, libisofs, a manipulation library for ISO 9660 filesystems, and libisoburn, a ISO 9660 multi-session library. On top of them there is cdrskin, a cdrecord emulator, and xorriso, a all-in-one application for ISO 9660 multi-session operations which additionaly provides a limited emulation of mkisofs.