TreeDyn is a tree visualization and annotation tool designed for the analysis of trees in biodiversity, phylogeny, and structure/function studies. It allows users to manage multiple trees and windows, export graphics in various formats, and use annotations to enhance tree analysis. The tool supports dynamic graphical methods for editing and analyzing multiple trees, including the projection of texts or symbols on leaf labels or nodes, highlighting of graphical elements based on queries or selections, and the use of scripts for automating tasks. TreeDyn also includes a command line interpreter for online tree building and a library of packages for specific research fields. The tool uses a 2D Euclidean space representation to organize tree items without superposition. TreeDyn is implemented in Tcl/Tk and is available for macOS, Linux, and Windows. It allows the management of collections of trees, enabling users to resize, organize, and switch configurations. TreeDyn supports the linking of annotations to tree elements, facilitating the identification and localization of tree elements based on leaf labels or annotation files. The tool also includes a SQL-like interpreter for querying annotations and performing highlighting operations. TreeDyn is under active development and is available under the GPL license. It provides a comprehensive solution for tree visualization, annotation, and analysis, with a focus on integrating meta-information to aid in the interpretation of tree data.TreeDyn is a tree visualization and annotation tool designed for the analysis of trees in biodiversity, phylogeny, and structure/function studies. It allows users to manage multiple trees and windows, export graphics in various formats, and use annotations to enhance tree analysis. The tool supports dynamic graphical methods for editing and analyzing multiple trees, including the projection of texts or symbols on leaf labels or nodes, highlighting of graphical elements based on queries or selections, and the use of scripts for automating tasks. TreeDyn also includes a command line interpreter for online tree building and a library of packages for specific research fields. The tool uses a 2D Euclidean space representation to organize tree items without superposition. TreeDyn is implemented in Tcl/Tk and is available for macOS, Linux, and Windows. It allows the management of collections of trees, enabling users to resize, organize, and switch configurations. TreeDyn supports the linking of annotations to tree elements, facilitating the identification and localization of tree elements based on leaf labels or annotation files. The tool also includes a SQL-like interpreter for querying annotations and performing highlighting operations. TreeDyn is under active development and is available under the GPL license. It provides a comprehensive solution for tree visualization, annotation, and analysis, with a focus on integrating meta-information to aid in the interpretation of tree data.