Listed below are some free plain WordPress themes that can be used for most any type of website. Most of these are white WordPress themes. I tried to find themes that are mobile devices compatible and made a note of it on each listing. Plain themes are easy to navigate, modify and have a clean feel.
If you didn't already know, WordPress has a complete listing of all its free themes. New themes are created, and old themes are updated regularly. I love to use plain themes as a reference when creating more complex themes. I've also noticed that there're not many options to find 'plain themes' on WordPress.org since the search options are left wanting. I've searched through the entire database to make a current list of the simplest, mot plain themes WordPress.org has to offer.