We just release F3D 4.0.0, fast and minimalist 3D viewer. Obviously free and open source

One of the key new feature is the support for .FCStd files! Quickly browse through your FreeCAD files effortlessly, generate thumbnails in your file browser as well.

https://github.com/f3d-app/f3d/releases/tag/v4.0.0

You can even open them on your web broswer right here:

https://f3d.app/viewer

Let us know what you think!