Brush is a 3D Gaussian Splatting engine for real-time rendering and training of 3D scenes from multi-view images. It features a modular Rust workspace architecture with applications for desktop GUI (eframe/egui), headless CLI, C FFI, and WebAssembly (web). The system loads datasets (COLMAP, Nerfstudio, RealityCapture), initializes and optimizes Gaussian splats via gradient descent using the Burn tensor library for autodiff, and renders via a wgpu-based rasterization pipeline. Key innovations include a GPU-accelerated radix sort for depth ordering, an actor model for async processing, and a virtual file system for cross-platform file access.