You can get Fate Core, Fate Accelerated, and the System Toolkit I believe all in ePub/Mobi format. And Core/Accelerated are on a pay what you want, so you can get it free if you like.
Personally, I love the idea of ebooks for RPGs, but find them problematic. The small file size and scalability of the text is fantastic! But when using it for a reference book isn't the best. With a PDF or physical book, you can say, "On page XX, it says this." Ebooks don't have page numbers. Granted, it's easier to do a search for specific text within an ebook, so that may be a moot point.
Also, the lack of physical pages is a difficult hurdle to get over. When reading the ebook you don't have that "Page 18 of 237" in the corner of your screen letting you know how far into the book you are. Pages, whether physical or digital, give readers a sense of scale; a sense of progress. Page count is the standard method of talking about how big a specific book is. Fate Accelerated is 48 pages, digest size. I say that and most people know what size to expect when they see it. But if someone were to tell you that Fate Accelerated is "only 14,000 words," a majority of people have no concept of what that would look like, either on the page or in-hand.
One of the biggest upsides of ebooks is also it's greatest weakness: it's an HTML file. That means no file-bloat for fancy background pictures or page decorations. But that also means no fancy background pictures or page decorations! Layout means nothing in ebooks, since it's all flowing text. Sure, it'll make the tables fit somehow, and turning the device landscape makes it easier to read them, but sidebars are now all inline text, and pictures are too! This means that you can't have text side-by-side with an image.
As a gamer, I'm all for ebooks. PDFs are such huge files! But as a layout guy…I like my fixed-dimension "archaic" pages, even if they are digital ones.