AI is the default image format used by Adobe Illustrator to save image data and AI files contain paths connected by points, instead of bitmap image data. AI files can also be easily enlarged without any quality loss.
In order to open their AI files, users will need to install Adobe Illustrator or find an image viewer that features built-in support for this particular graphic format.
One should be awarre that some utilities might rasterize the image because they will need to convert the vector data to a bitmap format to be able to display it.
There are numerous apps that will allow their users to view AI images and export them to more common graphic formats, thus being able to manage them with greater ease.