At Leanpub, we only sell ebooks, so they're available instantly, and have free updates, with no shipping costs like there are for delivering print books.
All our ebooks are DRM-free, and most are available in PDF, EPUB and MOBI. The formats available are shown on each book landing page; here is an article with some more information on available formats: http://help.leanpub.com/en/articles/2921549-what-formats-do-leanpub-books-come-in.