Snort is a network intrusion detection and prevention system. It is the most widely deployed technology of its kind in the world. It performs detection using a variety of methods including rules-based detection, anomaly detection, and heuristic analysis of network traffic. Its rules language is open source and available to the public as well.
TightVNC is a VNC distribution with many new features, improvements, and bugfixes over VNC. It is optimized for faster operation on slow network links such as modem connections, provides more configuration options in the server, features automatic SSH tunneling in the Unix vncviewer, and more. The modified servers and viewers are fully compatible with the original VNC software.
rsync is a replacement for rcp (and scp) that has many more features. It uses the "rsync algorithm" which provides a very fast method for remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand.
ntopmg is a network probe that shows network usage in a way similar to what top does for processes. It acts as a Web server, creating an HTML dump of the network status. It sports a flow collector, an HTTP-based client interface for creating ntop-centric monitoring applications, and RRD for persistently storing traffic statistics. Its C++ core can be scripted in Lua, for changing the appearance and extending functionality.
GNUnet is a peer-to-peer framework with focus on providing security. All peer-to-peer messages in the network are confidential and authenticated. The framework provides a transport abstraction layer and can currently encapsulate the network traffic in UDP, TCP, HTTP, HTTPS, or direct 802.11 (WLAN). GNUnet supports accounting to provide contributing nodes with better service. The services built on top of the framework include anonymous file sharing and a virtual network providing IPv4-IPv6 transition via protocol translation over the P2P network.
web2ldap is a full-featured Web-based LDAPv3 client written in Python. It is designed to run either as with stand-alone built-in Web server or under the control of another Web server with FastCGI support (e.g. Apache with mod_fastcgi). It has support for various LDAPv3 bind methods and a powerful built-in schema browser. HTML templates are supported for displaying and editing entries, and LDIF templates can be used for quickly adding new entries. A built-in X.509 parser displays a detailed view of certificates and CRLs with active links.
Unison is a file-synchronization tool for Unix and Windows. It allows two copies of a collection of files and directories to be stored on different hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other. Unison can deal with updates to both replicas of a distributed directory structure. Updates that do not conflict are propagated automatically. Conflicting updates are detected and displayed. Unison can communicate through a direct socket link or through an rsh/ssh tunnel. It uses network bandwidth efficiently.