how can we get site details

Site URLs may betray the framework and/or programming language but cannot be relied upon
HTTP response headers, cookies, stylesheets and source comments may also give clues.
Some nice tools for querying site details.

Some Good Sites 

• BuiltWith
• DomainTools
• NetCraft
• W3Techs
• SimilarTech

Firefox addons:

• Wappalyzer - CMS, frameworks/libraries, e-commerce, message boards etc.
• Domain Details - IP, country and webserver details
• Library Detector - Javascript libraries in use

Chrome Extensions:

• Wappalyzer
• SimilarTech
• PageXray

Bookmarklets:

• WTFramework - shows Javascript framework in use