Kernl is a services that provides private plugin and theme updates for WordPress. This is best illustrated with an example. Lets say that you have a brand new plugin that you are selling. Since you are selling this plugin, you can't host it via WordPress.org because otherwise people could download it for free.

Like any good developer, you want your plugin to be integrated with the automatic update functionlity of WordPress. Thats where Kernl comes into play. By simply adding a file to your plugin and shortcode snippet you'll be able to host your updates through Kernl instead of WordPress, therefore giving your users the best possible experience and timely updates.