Foxhound is a react-based WordPress theme, developed using the REST API available in WordPress 4.7. This theme turns your website into an app making your posts and pages load instantly.
Foxhound is the first REST API based theme in the WordPress theme repository. So it requires WordPress 4.7 or higher. Since there is no endpoint for menus in the current WordPress REST API, this theme recommends that you install a plugin for that functionality (e.g. WP API Menus).
If you want to check out this theme feel free to visit the Foxhound theme page.