Theses viewers are a part of my GitHub website: https://githubdragonfly.github.io/.
Not really looking to compete with any other viewers out there, just posting it in case if anybody might find anything useful there.
There is also a Texture Viewer which can show different image formats, either still or animated, as well as videos.
These are not necessarily perfect but are functional and do allow local file loading (blobs) as well as URL loading either via local server or from the Internet. Most viewers also provide for exporting the 3D model as an animated GIF and/or PNG (APNG).
The latest additions are Quick Viewer and ASSIMP Viewer and USDZ Viewer.
Quick Viewer, which is practically a simpler version of the Online 3D Viewer, is purely online based and its HTML file can be used as a standalone - just remove the line on top that calls the favicon.ico image file from my repository. Currently it supports the following 3D formats: 3DM, 3DS, 3MF, BIM, BREP, BRP, DAE, FBX, GLB, GLTF, IFC, IGES, IGS, OBJ + MTL, OFF, PLY, STL, STEP, STP, WRL.
ASSIMP(JS) based viewer supports even more formats: 3DS, 3MF, AC, AC3D, ACC, AMF, ASE, B3D, BLEND, BVH, COB, CSM, DAE, DRC, DXF, FBX, GLB, GLTF + BIN, HMP, IQM, IRR, KMZ, LWO, LWS, LXO, MD2, MD3, MD5MESH, MDC, MDL, MESH, MS3D, NFF, OBJ + MTL, OFF, OGEX, PLY, PMX, Q3O, Q3S, SIB, SMD, STL, X, XGL, ZGL.
BIM (dotbim) support was added to STEP Viewer.
Most viewers, if not yet all, also have mobile friendly version available.
Those who venture there to check this project out should read the posted descriptions.