Hello Nitish,
This is a really good question. Many people don’t know how to install a custom tab without using HTML: iframe tab. It is really simple and easy, need not be a geek to add a custom tab through developers.facebook.com/apps
For detailed explanation and step by step procedure on how you can add a Facebook Custom Tab for website please refer our article- http://bit.ly/17WQxAS

Let us know if this helped.
Regards,
Rucha