2019 update: There is now a new Matomo Analytics WordPress plugin available out called Matomo Analytics for WordPress. Plugin name: wp-matomo, not to be confused with the other plugin called WP-Matomo (WP-Piwik).
The difference between wp-matomo and WP-Matomo (WP-Piwik) is that this new plugin installs Matomo Analytics fully in your WordPress. Rather than having a plugin that connects your existing Matomo On-Premise or Matomo Cloud account with WordPress, you get the convenience of having a powerful analytics platform within your WordPress.
WP-Matomo (WP-Piwik) plugin
After six years of development, we are proud to announce the 1.0.0 release of our WP-Matomo WordPress plugin!
Started as a simple plugin to show a selection of statistics within the WordPress dashboard, WP-Matomo has become a full Matomo (Piwik) integration plugin. The plugin automatically adds the Matomo tracking code to your WordPress sites. The plugin displays your analytics reports directly within the WordPress admin panel. WordPress networks (“multisite”), CDN URLs and the proxy tracker for Matomo are also supported.
According to WordPress.org the plugin is being used by more than 50,000 WordPress sites!
This article explains how to install WP-Matomo and how to configure it to work with your Matomo instance.