Google VR View for the Web is a solid choice for web sites that need an embedded 360 image. Separate SDKs are available for Android and iOS. If you’re focused on Daydream or Cardboard for a VR experience, there is a VR Entry Flow. If you’re looking for a wide market of full VR headsets, A-Frame is a better choice. You can tell your clients you’re using Google VR technology and they’ll nod their heads. Google has a significant investment in VR and 360 image technologies.

Supported projections: equirectangular, stereo
License: Apache License 2.0
Distribution Method: Downloadable Library
Price: free

Google provides developers with two virtual reality (VR) platforms: Cardboard, the world’s most popular and accessible mobile VR platform, and Daydream, a new platform for low-latency, immersive, and interactive mobile VR. The Google VR SDKs include everything you need to develop for these platforms, including libraries, API documentation, developer samples, and design guidelines.

RICOH THETA recommended by Google as "very popular, relatively inexpensive solution for capturing mono 360° images and videos."

360° Media