I was searching on a google and found out that there is one site which contains all our questions and answers in same exact manner. So, i am just curious to know that what is happening here? If it's not stack related site then is it allow to fetch all data from stack site? Does this site have any permission to take those Q&As ?
The site you found is Column 80 - Plain Text optimised Stack Exchange, an old project by Mark Henderson (Mark is currently an employee of Stack Exchange, but the project predates his employment by several years). The Column80 site uses the Stack Exchange API to retrieve posts. As animuson pointed out, it does not provide sufficient attribution, which is unfortunate because it's a really cool project otherwise.
There are also numerous scraper sites, which are not as cool: they copy posts from Stack Exchange and try to monetize the traffic.