7-Zip is a free file archiver with high compression ratio. Its new 7z format with LZMA compression provides higher compression rates than other formats. But 7-Zip also supports the following formats:

• Packing / unpacking: 7z, XZ, BZIP2, GZIP, TAR, ZIP and WIM
• Unpacking only: ARJ, CAB, CHM, CPIO, CramFS, DEB, DMG, FAT, HFS, ISO, LZH, LZMA, MBR, MSI, NSIS, NTFS, RAR, RPM, SquashFS, UDF, VHD, WIM, XAR and Z

Furthermore, it includes a powerful File Manager. 7-Zip works in Windows but there are ports of the command line version for Linux/Unix and Mac OS X called p7zip. You can download 7-Zip from www.7-zip.org.

Git is a free & open source, distributed version control system designed to handle everything from small to very large projects (e.g. programming or LaTeX projects) with speed and efficiency.
Every Git clone is a full-fledged repository with complete history and full revision tracking capabilities, not dependent on network access or a central server. Branching and merging are fast and easy to do.
Furthermore, Git is available for Windows, Linux and Mac OS X and can be downloaded from http://git-scm.com/.
(Additionally, you may also want to take a look at GitSync.)

FreePDF (formerly known as FreePDF XP) is a tool for windows which lets you create and merge PDF-files. It installs a "virtual printer" for creating PDF-files from any other document. Furthermore, FreePDF comes with a graphical user interface for merging several PDF's into one file. FreePDF is distributed as "freeware" and can downloaded from http://freepdfxp.de.