Reall3dViewer is a high-performance 3D Gaussian Splatting (3DGS) web viewer built on Three.js. It streams and renders large-scale point cloud scenes (up to 150M points) at interactive frame rates across desktop and mobile devices. The viewer supports multiple input formats including PLY, SPLAT, SPX (proprietary high-compression format), SPZ, SOG, and GLB with the KHR_gaussian_splatting extension. Its architecture is event-driven and modular, with a central event system (Events.ts), dedicated loaders for each format, web workers for parallel data fetching and sorting, and a texture management pipeline that handles LOD tile streaming, frustum culling, and adaptive quality levels. Beyond basic viewing, the repository provides a full suite of interactive features: measurement and annotation tools (distance, area, point labels, 3D tags, circle plans), a map viewer (Reall3dMapViewer) with GIS basemap integration, a first-person/third-person player mode with physics (rapier3d), weather effects (rain, snow), audio-driven text overlays, and a fly-through camera path system. The code is published as an npm package (@reall3d/reall3dviewer) and includes comprehensive demo pages with scene configuration JSON files. While primarily an application library, the project also exhibits data/research characteristics through its custom SPX format specifications, advanced compression techniques (WebP, gzip, xz, zstd), and spherical harmonics support up to degree 3. The source code demonstrates high engineering craftsmanship in areas like GLSL shader modularization, WebAssembly integration for format parsing, and efficient web worker communication patterns. However, there are some maintenance risks including a large monolithic event constant file (200+ auto-incremented integers), hardcoded demo URLs, and a build script that embeds worker code as base64, which complicates debugging. No automated tests are present.