Apache JMeter is an open-source and powerful tool used for performance and load testing of web applications. With its friendly user interface, it allows developers to easily create and execute tests to measure the performance of an application. It also supports a wide range of protocols such as HTTP, SOAP, FTP, JDBC, JMS, and more. In addition, JMeter supports distributed testing, which can simulate a larger load on a system than would be possible with a single machine. This makes it an invaluable tool for performance tuning and optimization of web applications. JMeter is an essential tool for any developer looking to ensure their applications are running smoothly and efficiently.