Parasite is a debugging tool similar to Firebug, designed for use with GTK+ applications and available on GitHub. It allows users to modify application logic in real-time, even while the program is running, by using an embedded Python shell that facilitates direct interaction with the application's UI, irrespective of the original programming language. The tool provides a dynamic environment for developers to experiment and refine application functionality, and the site hosting Parasite is optimized for viewing in Firefox. Created by Chris Wanstrath, Parasite offers a unique approach to application debugging and development.