IBM Rational ClearCase is a software configuration management tool used in software development to manage source code files, build artifacts, and other software assets. It provides version control functionalities, allowing developers to track changes, collaborate on code, and maintain the integrity of the software. It also facilitates team collaboration, allowing multiple developers to work on the same codebase simultaneously. IBM Rational ClearCase is widely used in large-scale software projects and is particularly well-suited for complex development environments.