Arduino is an open-source hardware and software platform widely used in IoT prototyping and development. It provides microcontroller boards that are easy to program with the Arduino IDE. Many IoT projects use Arduino for sensor data collection, actuation, and MQTT-based communication. Its ecosystem includes thousands of libraries, shields, and community-contributed resources. Arduino is especially popular for education, hobby projects, and early-stage IoT solutions. While less powerful than industrial microcontrollers, its simplicity and affordability make it a cornerstone of IoT experimentation.