High performance image processing libraries for Java

http://java.sun.com/products/java-media/jai/

Setuid version of jexec to allow normal users access to jails

https://github.com/Intermedix/jailme

Perl/awk/sh regular expressions for Java

https://jakarta.apache.org/oro/

Build utility like make(1)

http://www.perforce.com/jam/jam.html

Compact Java virtual machine

http://jamvm.sourceforge.net/

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

Just Journal for Java blogging app

https://www.justjournal.com/

Reference Implementation of JSR 919

https://javaee.github.io/javamail/

JSW enables a Java application to be run as a Unix daemon

https://wrapper.tanukisoftware.org/

Wrapper script for various Java Virtual Machines

Java XPath Engine

https://jaxen.org

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/

Java library for accessing and manipulating XML documents

http://www.jdom.org/

Mainline variant of Kademlia Distributed Hash Table (DHT)

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

Powerful programmer\x27s text editor written in Java

http://jedit.sourceforge.net/

Open-source continuous integration server

https://jenkins.io/

Open-source continuous integration server

https://jenkins.io/

JetBrains CLion IDE

https://www.jetbrains.com/clion/

Free and open source typeface for developers

https://www.jetbrains.com/lp/mono

jf Open Huninn by justfont

https://justfont.com/huninn/

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/

Java access to native shared libraries

https://github.com/twall/jna

Joe's Own Editor

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

Dynamic web content management system (CMS)

https://www.joomla.org/

Dynamic web content management system (CMS)

https://www.joomla.org/

SIMD-accelerated JPEG codec which replaces libjpeg

https://libjpeg-turbo.org/

Lightweight and flexible command-line JSON processor

https://stedolan.github.io/jq/

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/

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

Kubernetes command-line tool

https://github.com/derailed/k9s

Makefile framework

http://svn.netlabs.org/kbuild

Free Unicode font for Sinhala script

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

Light-weight and easy-to-use password manager

https://keepass.info/

KeePass plugin which facilitates the Kee Firefox plugin

https://www.kee.pm/

Serial and network communications package

https://www.kermitproject.org/