Koin is a lightweight dependency injection framework for Kotlin developers. It simplifies the process of managing dependencies in an Android or Kotlin-based application by removing the need for complex configuration files. Koin is designed to be easy to use and integrates smoothly with Kotlin's features like coroutines and extensions. It allows developers to define modules for injecting dependencies in a declarative manner. Koin's simplicity makes it a popular choice for smaller projects and developers looking for a more intuitive dependency injection approach.