Current software development is often a cooperative activity, where different situations can arise that put the existence of a project at risk. One common and extensively studied issue in the software engineering literature is the concentration of a significant portion of knowledge about the source code in a few developers on a team. In this scenario, the departure of one of these key developers could make it impossible to continue the project. This work presents Knowledge Islands, a tool that visualizes the concentration of knowledge in a software repository using a state-of-the-art knowledge model. Key features of Knowledge Islands include user authentication, cloning, and asynchronous analysis of user repositories, identification of the expertise of the team's developers, calculation of the Truck Factor for all folders and source code files, and identification of the main developers and repository files. This open-source tool enables practitioners to analyze GitHub projects, determine where knowledge is concentrated within the development team, and implement measures to maintain project health. The source code of Knowledge Islands is available in a public repository, and there is a presentation about the tool in video.