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/

JDBC connection pool

http://www.bitmechanic.com/projects/jdbcpool/

Mainline variant of Kademlia Distributed Hash Table (DHT)

http://www.pps.univ-paris-diderot.fr/~jch/software/bittorrent/

Open-source continuous integration server

https://jenkins.io/

Converts JFile database to CSV, and vice versa

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

Simulates a jigsaw puzzle and illustrates the use of clipping paths

http://gap.nongnu.org/jigsaw/

Java source to byte-code compiler made available by IBM

http://jikes.sf.net/

English to Japanese dictionary for GNUstep

http://www.eskimo.com/~pburns/Dictionaries/

Command line client for posting JustJournal entries

https://www.justjournal.com/

Jerry's command-line LiveJournal.com entry system

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

Jim Knoble's font package for X

http://www.jmknoble.net/fonts/

Joe's Own Editor

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

Dynamic web content management system (CMS)

http://www.joomla.org/

IJG's jpeg compression utilities

http://www.ijg.org/

View and/or control a remote PC

http://jrdesktop.sourceforge.net/

JSON (JavaScript Object Notation) implementation in C

https://github.com/json-c/json-c/wiki

JSON (RFC 4627) interface for Glib

http://live.gnome.org/JsonGlib

JSON reader and writer library for C++

https://github.com/open-source-parsers/jsoncpp

General purpose dynamic array

http://judy.sourceforge.net/

Regression testing utility for use with the Java(TM) Language

http://www.junit.org/

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/

802.11 layer2 wireless network detector, sniffer, and IDS

http://www.kismetwireless.net/

Authentication system developed at MIT, successor to Kerberos IV

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

Cracks SAMBA or Windows NT passwords

Linux Audio Developer's Simple Plugin API

http://www.ladspa.org/

Fast MP3 encoder kit

http://lame.sourceforge.net/

Tetris-like game for GNUstep

http://www.nongnu.org/gap/lapispuzzle/

Image viewer and slideshow application

http://gap.nongnu.org/

LaTeX service for GNUstep

http://www.roard.com/latexservice/

Microsoft .CABinet file creator

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

Light Color Management System -- a color management library

http://www.littlecms.com/

Accurate, fast, and small-footprint color management engine

https://www.littlecms.com/

Utility for patching LDAP directories using LDIF files

https://launchpad.net/ldapdiff

Ldconfig compatibility script

Library for programs conforming to DNS RFCs and drafts

https://www.nlnetlabs.nl/projects/ldns/

LALR(1) parser generator. Similar in function to yacc and bison

https://www.hwaci.com/sw/lemon/

Better pager utility

https://www.greenwoodsoftware.com/less/

Archive files using LZSS and Huffman compression (.lzh files)

http://www2m.biglobe.ne.jp/~dolphin/lha/lha.htm

Archive files using LZSS and Huffman compression (.lzh files)

https://lha.osdn.jp

OpenEGL library

http://www.freedesktop.org/Software/xorg

The FS library

https://www.x.org/

OpenGL library that renders using GLX or DRI

http://www.freedesktop.org/Software/xorg

OpenGL utility library

http://www.freedesktop.org/Software/xorg

OpenGL widgets library

http://www.mesa3d.org/

Inter Client Exchange library for X11

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

Library for creating trees of CORBA IDL files

http://www.gnome.org/