Network tools and helpers

Whois client:
Source to a whois client (for unix) which defaults to whois.apnic.net.
Looking glass sites:
Check the global routing table for the specified IP address or AS number.
IRRToolSet:
Suite of policy analysis tools.
IPMA project:
Merit Network's group of internet analysis tools, including real-time graphs of current Internet routing instability.
Geektools:
A web site featuring a range of network tools and resources.
IP address calculator:
An open-source java-based tool that assists network administrators to calculate IPv4 and IPv6 address space. A handy whois client is also included.