Whois
Finds contact information for the owner of specified domain/IP.
Common Uses:
- To Track Down Spammers
- To Get Contact Info for the Owner of a Domain
- To Report a Problem with a Domain

Spam Database Lookup
Check IP addresses in RBL databases.

DNS Bajaj
A tool mainly for checking the delegation of a domain. As the name implies (or at least I hope so) it does this by making a graph of the interrelationships beteween all the nameservers involved in the managment of the domain and marking the servers that does funny stuff in a way that makes it easy to pinpoint them by sight - by eye if you want to.

DIG DNS
Provides information about the DNS entries associated with a specified domain or hostname (such as A record or MX record entries). Common Uses:
- To Verify your DNS Entries
- To Find Mail Servers for a Domain

IP Calculator
This tool is designed to show you information about a CIDR range, like 192.168.0.0/16 (such as the netmask to use, and the lowest and highest IPs in the range). However, you can also enter a single IP address such as 192.168.114.112 and see all the possible CIDR ranges, or enter just a CIDR such as /24.

Ping
Tests how long it takes for packets to get from our web server to the specified host.

IP Subnet Chart
Useful IPv4 CIDR table