WordPress Plugins extend WordPress to do almost anything you can imagine. There is a free, community-contributed plugin directory where you can find, download, rate, and receive support on almost 30,000 free plugins for WordPress.
Besides the free WordPress plugin repository, there are also thousands of other premium (paid) plugins. Most cost just $10-$20 on a one-time basis. Others are free plus a monthly subscription. Our favorite repository for premium WordPress plugins is CodeCanyon.
You Get What You Pay For
Keep in mind that many of the free WordPress plugins are simply amazing, but some are down right terrible. The old adage that you get what you pay for applies. Free plugins are almost never as good or as powerful as their paid/premium brothern.
The WordPress Plugin API
Because WordPress is open source, anybody can write their own plugin in the event one doesn’t already exist. There’s tons of documentation from WordPress on the Plugin API as well as numerous resources on the web.