4) Rewriting yoursite.com/user.php?username=xyz to yoursite.com/xyz
Have you checked zorpia.com.If you type http://zorpia.com/roshanbh233 in browser you can see my profile over there. If you want to do the same kind of redirection i.e http://yoursite.com/xyz to http://yoursite.com/user.php?username=xyz then you can add the following code to the .htaccess file.
5) Redirecting the domain to a new subfolder of inside public_html.
Suppose the you’ve redeveloped your site and all the new development reside inside the “new” folder of inside root folder.Then the new development of the website can be accessed like “test.com/new”. Now moving these files to the root folder can be a hectic process so you can create the following code inside the .htaccess file and place it under the root folder of the website. In result, www.test.com point out to the files inside “new” folder.