Jakarta Commons HttpClient
The Jakarta Commons HttpClient component provides an efficient, up-to-date, and feature-rich package implementing the client side of the most recent HTTP standards and recommendations.

Jakarta Commons Net
Jakarta Commons Net implements the client side of many basic Internet protocols. The purpose of the library is to provide fundamental protocol access, not higher-level abstractions. Therefore, some of the design violates object-oriented design principles.

JFTP
JFtp is a graphical Java network and file transfer client.
It supports FTP using its own FTP API and various other protocols like SMB, SFTP, NFS, HTTP, and file I/O using third party APIs, includes many advanced features such as recursive directory up/download, browsing FTP servers while transferring files, FTP resuming and queueing, browsing the LAN for Windows shares, and more.

jIRCii
jIRCii is an Internet Relay Chat client (IRC) for Windows, MacOS X, and Linux. jIRCii provides an irc experience similiar to ircii, hADES, and BitchX with the advantages of a solid user interface. Features include DCC/CTCP support, multiple server connections, IRC over SSL support, tab key nickname completion, and over 75 built-in commands. jIRCii is fully scriptable using sleep, a Perl-like language.

JSch
JSch is a pure Java implementation of SSH2. JSch allows you to connect to an sshd server and use port forwarding, X11 forwarding, file transfer, etc., and you can integrate its functionality into your own Java programs. JSch is licensed under BSD style license.

JXplorer
JXplorer is an open source ldap browser originally developed by Computer Associates' eTrust Directory development lab. It is a standards compliant general purpose ldap browser that can be used to read and search any ldap directory, or any X500 directory with an ldap interface. It is available for immediate free download under a standard OSI-style open source licence.

PlanetaMessenger.org
PlanetaMessenger is the universal Instant Messenger fully written in java. Some PlanetaMessenger.org features are: Plugin support for many IM networks like, ICQ, AIM, MSN, ComVC, Yahoo, Jabber and so on; Multi-profile support.

Smack
Smack is an Open Source XMPP client library for instant messaging and presence.

SSL-Explorer
SSL-Explorer is the world's first open-source SSL VPN solution of its kind. This unique remote access solution provides users and businesses alike with a means of securely accessing network resources from outside the network perimeter using only a standard web browser.