IEM Plug-in Suite
plugins.iem.at
The IEM Plug-in Suite is a free and Open-Source audio plugin suite including Ambisonic plug-ins up to 7th order created by staff and students of the
Institute of Electronic Music and Acoustics.

The IEM is an awesome suite of tools. I’ve used it to decode ambisonic recordings, but also to create nice spatial effects for stereo sound design. If you’re not familiar with ambisonic, it is now the main technic use for VR spatial sound.