Bonsplit is a library designed for macOS apps, focusing on creating customizable tab bars and layout splits. It offers smooth 120fps animations, drag-and-drop reordering of tabs, and full support for SwiftUI and keyboard navigation. The library allows developers to create tabs with optional icons and indicators to show if a tab has unsaved changes. It also supports splitting panes both horizontally and vertically, giving developers the ability to organize their workspace effectively. Tabs can be updated at any time, with changes animating smoothly. Developers can programmatically navigate between panes using directional commands. Bonsplit supports two-way synchronization with external applications, allowing users to query layout geometry and receive notifications about changes. The library provides a complete set of structures for managing layout snapshots, pane geometries, and tab information, all of which are designed to be thread-safe and easily serializable. Configuration options allow developers to customize behavior and appearance, such as enabling split buttons or setting minimum pane dimensions. There are also presets for different configurations, including a single-pane mode for simpler applications. The library ensures flexibility through its various settings, catering to the needs of different app designs and user experiences.