FSPViewer is a free tool to view 360 images from the camera.
It is comparable to the RICOH THETA desktop application viewer.
You may see the following error.
FSPViewer-2.1.0-64$ ./FSPViewer64 ./FSPViewer64: error while loading shared libraries: libpng12.so.0: cannot open shared object file: No such file or directory
You can get the required libpng12.so.0 library from linuxuprising.
sudo add-apt-repository ppa:linuxuprising/libpng12 sudo apt update sudo apt install libpng12-0
Drag and drop file onto FSPViewer