A file with an .ai extension is an Adobe Illustrator Artwork file that contains vector graphics on a single page. It uses points to create paths for displaying the image data, thus making it safe from losing image quality if it is enlarged. AI format finds its major usage for logos and print media. AI files can be opened with Adobe Illustrator, Adobe Acrobat DC, PaintShop Pro, and CorelDraw Graphics tools.
Files with .EPUB extension are an e-book file format that provide a standard digital publication format for publishers and consumers. The format has been so common by now that it is supported by many e-readers and software applications. For example, on Mac OS, the pre-installed Books software provides the support for opening such files. In addition, there are a lot of compatible software available for smartphones, tablets and computers.
You can also convert AI into many other file formats. Please see the complete list below.