MetaWin 3 is a new version of the open-source software for meta-analysis, developed by Michael S. Rosenberg from the Center for Biological Data Science at Virginia Commonwealth University. The software aims to fill the gap left by the abandonment of earlier versions, which were primarily written in Pascal and Delphi, and were limited to the Windows operating system. MetaWin 3 is written in Python, making it multi-platform, and is available under a GPL-3.0 license. It includes standardized effect size calculations, exploratory and publication bias analyses, and supports both simple and complex explanatory models, including meta-regression. The software provides an intuitive GUI for novice analysts and users, with pre-compiled executables for Windows and macOS available on the MetaWin website. The codebase is openly available on GitHub, and the help manual is accessible on the MetaWin website. MetaWin 3 supports various output formats, including text, HTML, markdown, and standard graphical formats, and includes features such as auto-generated captions and references to aid in interpretation. The software has been cited thousands of times across various fields and continues to be a popular tool for meta-analytic research.MetaWin 3 is a new version of the open-source software for meta-analysis, developed by Michael S. Rosenberg from the Center for Biological Data Science at Virginia Commonwealth University. The software aims to fill the gap left by the abandonment of earlier versions, which were primarily written in Pascal and Delphi, and were limited to the Windows operating system. MetaWin 3 is written in Python, making it multi-platform, and is available under a GPL-3.0 license. It includes standardized effect size calculations, exploratory and publication bias analyses, and supports both simple and complex explanatory models, including meta-regression. The software provides an intuitive GUI for novice analysts and users, with pre-compiled executables for Windows and macOS available on the MetaWin website. The codebase is openly available on GitHub, and the help manual is accessible on the MetaWin website. MetaWin 3 supports various output formats, including text, HTML, markdown, and standard graphical formats, and includes features such as auto-generated captions and references to aid in interpretation. The software has been cited thousands of times across various fields and continues to be a popular tool for meta-analytic research.