The ebooks are available in Epub and Bilbary is currently working on a browser based reading app as well as apps for Android, iOS.
When Bilbary was first announced last December, it was pitched as a rental service. That didn't come to past, unfortunately, because publishers simply didn't warm to the idea (except for the ones who have signed with Afictionado or launched Skoobe). They much preferred to sell ebooks, not rent them.
This means Bilbary is really not much more than just another ebookstore, so you have to wonder why so many publishers signed up (including 7 of the Big 8). I can explain it in one word: analytics. Bilbary is going to share data about their customers with publishers. This could range from something as simple as the number of pages read to more complex details.
Bilbaary is also planning to expand into more markets and add some ebook rentals later this year, but those will mainly come from academic publishers. Rental selection will probably be similar to that found in the Kindle Store and elsewhere (textbooks, mainly).