I’ve tried to download the OpenNI-2.3.0.55.zip a few times, Windows 10 keeps showing it as invalid and won’t open it. There is an earlier version available on GitHub, OpenNI-Windows-x64-2.2, but for me at least that NIViewer is not recognizing the Orbbec devices.
Going from memory here but I believe the files that you can’t open are Linux or Android files so they can be skipped. Pretty sure I managed to open the zip file with winzip or something similar and just pull out the win32 and 64 folders.
I had the same issue. The windows zip utility has problems with that zip. Use a different zip utility such as WinZip, 7-Zip, etc…