GLB is glTF packed into a single binary file - geometry, materials, textures and a node hierarchy in one blob. It is the format the web actually uses for 3D, and the one most viewers, AR tools and game engines want.
Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a GLB file above and choose afterwards.