Rewrite to a folder and hide the folder name in url :

RewriteCond     %{SERVER_NAME}    ^sitename.com        [NC,OR]
RewriteCond    %{SERVER_NAME}    www.sitename.com    [NC]
RewriteCond    %{REQUEST_URI}    !^anyfiletoexclude.php    [NC]
RewriteCond    %{REQUEST_URI}    !^/foldertoredirect/    [NC]
RewriteCond    (.*)        /foldertoredirect/$1

force use www

RewriteCond    %{SERVER_NAME}    ^website.com$
RewriteRule    ^/(.*)        http://www.website.com/$    [L,R]