Zopfli Compression Algorithm

https://github.com/google/zopfli

Swiss army knife for the serious backup manager

https://github.com/fcorbelli/zpaqfranz

Zooming photo album generator

http://namazu.org/~satoru/zphoto/

ZFS based replication and failover solution

http://www.bolthole.com/solaris/zrep/

Z shell

https://www.zsh.org/

Tool for managing Zshell plugins inspired by Vundle

https://github.com/zsh-users/antigen

Fish-like autosuggestions for Zsh

https://github.com/zsh-users/zsh-autosuggestions

Additional completion definitions for Zsh

https://github.com/zsh-users/zsh-completions

Curses-based tools for Zshell, e.g. multi-word history searcher

https://github.com/psprint/zsh-navigation-tools

Fish shell syntax highlighting for Zsh

https://github.com/zsh-users/zsh-syntax-highlighting

Interactively transferring files to a remote machine while using ssh

http://zssh.sourceforge.net/

Fast real-time compression algorithm

https://facebook.github.io/zstd/

C++ header-only ZLib wrapper

https://github.com/mateidavid/zstr

A file transfer program

http://zsync.moria.org.uk/

Platform-independent object-oriented C++ threading library

http://zthread.sourceforge.net/

Display ZFS dataset I/O in real time

https://github.com/asomers/ztop

Simple ncurses based pseudo-3D driving game

Utilities for searching in bzip2, gzip, lzip, and xz archives

http://www.nongnu.org/zutils/zutils.html

Easily and reliably transfer ZFS filesystems

https://github.com/allanjude/zxfer

C++ library for linear/matrix barcode recognition

https://github.com/zxing-cpp/zxing-cpp

ZFS Administration GUI

https://github.com/manoeldesouza

Library to provide transparent read access to zipped files

https://github.com/gdraheim/zziplib