Whois is a means of looking up names in a remote database. Used initially as an aid for finding e-mail addresses for people at large institutions or companies. In the domain name world, whois services are used to find out the status and details of a specific domain name. 

whois is a program that will tell you the owner of any second-level domain name who has registered it in any of the domain registrars. 

Network Solutions & Verisign:

In the past all registrations were done by network solutions. Later Network Solutions was acquired by Verisign.

whois can also be used to find out whether a domain name is available or has already been taken. If you enter a domain name you are considering to buy and the search result is show up as available, domain name is likely to be available and you can apply to register it.

Few years back, the ICANN (Internet Corporation for Assigned Names and Numbers) has opened up domain name registration to a number of other companies. To search all of these companies at the same time for registration information, you can use betterwhois.

whoi.sc 

This is a remarkable free service where you can monitor the domain names of interest. They also have a tool to receive domain name suggestions. Whis.sc, accessible through website whois.sc is a service that helps you investigate thoroughly about any website in question.

You can do a simple registration on the site and add lot of domains for monitoring. They will send you e-mail notifications on the basis of the changes taking place to the status of these domains.

The Whois Source Domain Explorer lets you search for domain information in several ways. Among domain lookup services, whois.sc is really distinct due the many features they offer which other lookups do not.