GNU version of the traditional tape archiver

http://www.gnu.org/software/tar/

Interactive typing tutor

http://www.gnu.org/software/gtypist/

Compression utility designed to be a replacement for compress

http://www.gnu.org/software/gzip/

gzip recovery toolkit

https://www.urbanophile.com/arenn/hacking/gzrt/

Anti-spam / denial of service counter-measure tool

http://www.hashcash.org/

Automatically generating simple manual pages from program output

https://www.gnu.org/software/help2man/

High-color icon theme shell from the FreeDesktop project

http://www.freedesktop.org/Standards/icon-theme-spec

Network auditing tool

http://www.hping.org/

Hebrew spellchecker and morphology engine

http://hspell.ivrix.org.il

All W3C published SGML DTDs for HTML

Converts HTML documents into plain text

http://www.mbayer.de/html2text/

Time synchronization over http utility

http://www.vervest.org/htp/

Tool for measuring webserver performance

https://github.com/httperf/httperf

Improved spell-checker for Hungarian and other languages

https://hunspell.github.io/

IA64 simulator (Intel(R) Architecture 64)

http://www.boo.net/~jasonp/

Restricted unix shell

http://ibsh.sourceforge.net/

ICE authority file utility for X

Utilities of the Tango project

http://tango-project.org/

International Components for Unicode (from IBM)

http://site.icu-project.org/

Library to handle internationalized domain names

https://www.nic.ad.jp/ja/idn/idnkit/download/

Imake and other utilities from X.Org

https://www.x.org/

Input extension headers

Tools to internationalize various kinds of data files

http://www.gnome.org/

Performance Test of Sequential File I/O

https://www.iozone.org/

Performance Test of Sequential File I/O (older version)

https://www.iozone.org/

Tool to measure maximum TCP and UDP bandwidth

https://sourceforge.net/projects/iperf2/

KAME racoon IKE daemon, ipsec-tools version

http://ipsec-tools.sourceforge.net/

ISC Cron, former Vixie Cron

ftp://ftp.isc.org/isc/cron/

Lists of the country, language, and currency iso names

https://salsa.debian.org/iso-codes-team/iso-codes

Character entity sets from ISO 8879:1986 (SGML)

C library for encoding, decoding, and manipulating JSON data

http://www.digip.org/jansson/

Implementation of the codec specified in the JPEG-2000 standard

https://www.ece.uvic.ca/~frodo/jasper/

Updated Java timezone definitions

Wrapper script for various Java Virtual Machines

Decoder implementation of the JBIG2 image compression format

https://github.com/ArtifexSoftware/jbig2dec

Lossless compression for bi-level images such as scanned pages, faxes

https://www.cl.cam.ac.uk/~mgk25/jbigkit/

Converts JFile database to CSV, and vice versa

http://www.land-j.com/jfileu.html

Java source to byte-code compiler made available by IBM

http://jikes.sf.net/

Jerry's command-line LiveJournal.com entry system

http://umlautllama.com/projects/perl/#jlj

Joe's Own Editor

https://sourceforge.net/projects/joe-editor/

IJG's jpeg compression utilities

http://www.ijg.org/

General purpose dynamic array

http://judy.sourceforge.net/

The editor which sucks less

http://www.mirbsd.org/jupp.htm

Makefile framework

http://svn.netlabs.org/kbuild

KB extension headers

http://www.freedesktop.org/wiki/Software/xlibs

Serial and network communications package

https://www.kermitproject.org/

Authentication system developed at MIT, successor to Kerberos IV

http://web.mit.edu/kerberos/

Official AT&T release of KornShell 93

http://www.kornshell.com/

Linux Audio Developer's Simple Plugin API

http://www.ladspa.org/

Microsoft .CABinet file creator

http://ohnopub.net/~ohnobinki/lcab/