glTF is a file format for 3D models. glTF files use the .gltf extension. The glTF format stores data in JSON text. The JSON can contain binary blobs known as buffers. Buffers store data like meshes and images. glTF files may also reference external image files. The binary .glb format also has JSON text. But blobs can append directly to the file.
glTF file sizes are compact. The JSON file description parses quickly. Large data like geometry and textures store in binary. Binary files are smaller than text. glTF does not mandate any runtime behavior. It is a pure asset format.
A glTF file may use .gltf or .glb extensions. Both reference external binaries and textures. Or they directly embed data as base64 strings or raw byte arrays. glTF 2.0 incorporated .glb into the standard. GLB before was an extension in glTF 1.0.
glTF shares 3D assets across software. Many applications support rendering glTF 3D scenes. glTF uses JSON for portability. Its advantages include compact size and runtime-independence. The Khronos Group develops and releases the format.
Blender
Microsoft Paint 3D
Sketchfab