Domtools is a set of Unix shell commands that allow you to traverse DNS domain hierarchies, list all hosts (or subdomains) within a given domain, convert a host name to an IP address and vice-versa, convert a normal IP address to "in-addr.arpa." format and vice-versa, and more. These commands can be used manually, or included as building blocks for higher level DNS tools. Output is easily computer parsable.
Angel is a simple yet useful tool to monitor the services on your network. Technically speaking, it's a Perl program that runs every 'n' minutes (usually fired from your cron) and calls different perl subprograms (referred to as "plugins" from now on) to do the actual testing. It will then generate an HTML table containing the status of your network.
curl and libcurl is a tool for transferring files using URL syntax. It supports HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, DICT, TELNET, LDAP, POP3, IMAP, SMTP, RTSP, RTMP, and FILE, as well as HTTP-post, HTTP-put, cookies, FTP upload, resumed transfers, passwords, port numbers, SSL certificates, Kerberos, and proxies. It is powered by libcurl, the client-side URL transfer library. There are bindings to libcurl for about 40 languages and environments.
LinPopUp is a GTK port of Winpopup, running over Samba. It permits communication with a Windows-running computer that runs Winpopup, sending or receiving messages. Please note that LinPopUp is not only a port, as it includes several enhanced features like it doesn't need to run permanently, full message base management, can be run minimized, full message editor capabilities, clipboard cut&paste, documentation, etc.
RabbIt is a mutating, caching Web proxy used to speed up surfing over slow links like modems. It does this by removing advertising and background images and scaling down images to low quality JPEGs. RabbIT is written in Java and should be able to run on any platform. It does depend upon an image converter if image scaling is on. The recommended image converter is "convert" from the ImageMagick package.
Spong is a simple system-monitoring package. It features client-based monitoring (CPU, disk, processes, logs, etc.), monitoring of network services, grouping of hosts (routers, servers, workstations, and PCs), host-specific contact and downtime information, configuration on a client-by-client basis, results displayed via the Web, history of problems, messaging (via email or pager) when problems occur, and verbose information to help diagnosis problems. It communicates via simple TCP-based messages, and is written in Perl.
The DECnet for Linux project aims to provide the kernel-level socket layer and a set of applications to allow Linux systems to participate in a DECnet phase IV network. It currently has an application library (suitable for building DECnet functionality into X11R6), file and terminal access.