BUI extracts Blender's UI and interaction code into a small C runtime with language bindings (Python, Rust, JavaScript, C/C++, Dear ImGui) so apps can use Blender's widgets, look, and highly optimized rendering without running Blender. It offers web-like HTML/CSS and component APIs, extensive widget support, and damage/GPU rendering for very low CPU, fast startup, and better performance than alternatives like gpui.