HTTP Time Protocol is a time synchronization tool that uses Web server responses (HTTP headers) instead of the NTP protocol. If you are behind a corporate firewall, NAT device, or proxy server, HTP will still be able to synchronize the time. For high precision time synchronization, use ntpd.
LFT (Layer Four Traceroute) is a sort of "traceroute" that often works much faster than the commonly-used Van Jacobson method and goes through many configurations of packet-filter based firewalls. More importantly, LFT implements numerous other features, including TCP, UDP, or ICMP-based traces, AS number lookups through several reliable sources, loose source routing, netblock name lookups, and more. LFT also distinguishes between layer-4 protocols, which make its statistics slightly more realistic, and gives a savvy user the ability to trace protocol routes, not just layer-3 hops.
Netcat is a simple Unix utility which reads and writes data across network connections, using TCP or UDP protocol. It is designed to be a reliable backend tool that can be used directly or easily driven by other programs time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
ipcalc takes an IP address and netmask and calculates the resulting broadcast, network, Cisco wildcard mask, and host range. By giving a second netmask, you can design sub- and supernetworks. It is also intended to be a teaching tool and presents the results as easy-to-understand binary values.
BixData is a cluster management tool that includes monitoring and system administration features. It monitors services (HTTP, ping, POP3, SMTP), performance, and processes. It has a management console for VMWare and Xen that supports multiple virtual machine hosts and guests. It can create critical notifications and send email alerts for any system event (HTTP, ping, CPU, memory, SMART diagnostics, VM stats). A graphical desktop supports real-time dynamic graphs. The runtime agents and server components are lightweight and easy to set up and run.
Pidentd v3 is a much improved version of the original Ident daemon both in terms of speed, code quality and features. Features include multithreading, a "configure" script, startup autodetection, much clearer/rewritten C code, doesn't run as root after startup, has a configuration file and can be started from /etc/inittab (on systems using a SysV init).
Host is a complete and powerful command-line based DNS query and testing tool. It has many of the same basic features as other similar tools such as nslookup and dig, but it has more extensive testing and test automation features. Host also has a much more standard (i.e. Unix-based) command-line user interface.
Very Simple Network Monitor is a bash shell script CGI that monitors a number of services on a network. It currently checks for node-up, TCP service up, and UDP service up. A service or system can be put in maintenance status to avoid repetitive alarms. It is easy to customize, trigger alarms by email, or whatever you like (depends on nmap for TCP/UDP service checks). Installation is also simple. It generates HTML with all statuses, and for all services just in one view.