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/

Humanist sans-serif font

https://www.theleagueofmoveabletype.com/junction

Unicode/MUFI OpenType font for medievalists (Latin, IPA, Runic, Greek)

http://junicode.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

Free Unicode font for Sinhala script

http://www.kaputa.com/slword/kaputaunicode.htm

Serial and network communications package

https://www.kermitproject.org/

Library for registering keyboard shortcuts

https://github.com/engla/keybinder

Library for registering keyboard shortcuts

https://github.com/engla/keybinder

Extra modules and scripts for CMake

https://quickgit.kde.org/?p=extra-cmake-modules.git

Khmer OS fonts

https://sourceforge.net/projects/khmer/

Browser based analytics and search interface to ElasticSearch

https://www.elastic.co/products/kibana

Web application framework for writing web APIs in C

http://www.kore.io/

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/

Testing framework for infrastructure software

https://github.com/jmmv/kyua/

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/

Linear Algebra PACKage

http://www.netlib.org/lapack/

Tetris-like game for GNUstep

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

Session management system for JACK audio applications

http://www.nongnu.org/lash/

Image viewer and slideshow application

http://gap.nongnu.org/

LaTeX service for GNUstep

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

Sans-serif type family

http://www.latofonts.com

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/

Maintain DNS zones using an LDAP directory

https://github.com/bklang/ldap2dns

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/

Long double math precision functions

http://www.moshier.net/

Revival of an old classic, Alternate Gothic #1

https://www.theleagueofmoveabletype.com/league-gothic

Revival of ATF\x27s classic Spartan

https://www.theleagueofmoveabletype.com/league-spartan

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

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

C library for efficient image processing and image analysis operations

http://www.leptonica.org/

Better pager utility

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

Fast and lightweight key/value database library by Google

https://github.com/google/leveldb

Fixed width fonts from the Linux Font Project

Variable width fonts from the Linux Font Project

Shell-like command line FTP client

http://lftp.tech/

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

The FS library

https://www.x.org/

OpenGL utility library

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