Apple's Quicktime, available for Macintosh and Windows, has been a pioneer in VR and still is one of the best performers. Quicktime is distributed at no cost and payment is only required if you want to use editing functions. Unfortunately, under Windows, Quicktime reminds the user of the need to upgrade to the Professional Version the first time it is run after a reboot. Some Windows users (particularly the majority who do not need Quicktime's editing functionality) find it a nuisance. As many Apple products, Quicktime is probably technologically ahead of most other competitors, but lacks the installed user base and third party software.
Although QuickTime is only available for Mac and Windows platforms, on Linux the Windows version can be installed via wine