By default Piwik comes with 20+ plugins which are officially maintained.
The Piwik developer community is starting to build plugins not officially supported by the Piwik team, but you can give them a try and report any problems you might experience:
There are also Plugins to integrate Piwik with your website.
Click on the image to learn more!
You can also use the Adobe AIR application to load your Piwik reports onto your desktop
A Piwik plugin is a ZIP file. Once you have downloaded the plugin, unzip it; it should create a directory ("YourPluginName"). Upload this directory under piwik/plugins and visit your Piwik admin interface to install the plugin. It's done! You can now enjoy your new plugin's features.
Please see the Piwik developer zone for more information, tutorials and examples.
Often Piwik plugins have their own trac ticket page. Please add a new comment on the plugin trac page to report any issue you might have with the plugin. If the plugin is not hosted on the Piwik trac, please contact the plugin author directly.