Huge Texture allows you to import and use textures larger than 8192x8192px in Unity.
When importing a texture, Huge Texture splits the texture into pages and saves it as a Texture Array. Texture Array is combined on the shader side, which does not create extra draw calls and has almost no effect on performance.
uPano (Unity Panorama Solution) is a universal multi-platform solution for displaying dynamic and static panoramas, and creating virtual tours.
uPano is very easy to learn and use, and is great for people who do not have programming experience.
Visual Tour Maker lets you create virtual tours in minutes.
In most usage scenarios, you can make interactive panoramas without creating your own scripts.
If you have some very specific purpose, uPano has a powerful and easy-to-use API that will allow you to implement any behavior.