[stevenmw]

 
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^([^/]+)/$ $1.php

replace .php with the extension you want to hide

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5}|/)$
RewriteRule (.*)$ http://www.example.com/yourdirectory/$1/ [R=301,L]

add trailing slash
you will need to reference your target directory for this to work properly