If you're going to be in the business of delivering digital publications; books, text books, magazines, newspapers and other formats; you need to address several areas, essentially at the same time:
Serving the digital content. This may be further complicated by any requirement to serve the content to specific users, i.e. you might have 'members' that purchase copies, these purchased may be downloaded onto various devices (computers, eReaders) but your users will also have a copy of record in their 'member accounts area'.
How will members read the digital content? Ideally your library will deliver content that can be read by whatever device or software service the member has such as: Calibre, Kindle, Adobe Acrobat or other PDF reader, Adobe Digital Editions reader software, Nook, etc.
If you are in the business 'for profit' you will need a means for charging customer/members, and for fulfilling or delivering purchases to member accounts and/or devices.
You will also need your content, the valuable digital content that your members will be prepared to pay for in some way to access via your service.
Your service will be like a digital library, where members will be able to login to their own accounts, see what they have borrowed or bought, and even search through the library, browsing copies in your system that they might borrow or buy.
Mathletics: A teacher can set up exercise for students to do math on computers at home. Uses gamefication idea to create a community move. Pricing €5 per student per year.
The big issue is product versus service. Publishers want to keep control (and fees).
Overdrive? Amazon loaning.
Random book page?
XBMC
Foobar2000
Can these be customised to deliver books?
Digital locker services, Dropbox, GoogleLS, Amazon S3.
REFERENCES AND OTHER SOURCES
SOPAC is an open source library discovery/catalogue service (link), this version is termed the social OPAC.
eBook options for online library services (link), a comparison of some solutions
Small Moves: Open Library Integrates Digital Lending (link) and the OpenLibrary site itself is here (link).
Scan My Library (link)
EBSCO host publishers aggregator (link)
Self hosting publications (link)
Adobe Digital Editions reader (link) and further links to the Adobe ecosystem of product/services.
A really nice, minimalist library site, the interface is at exactly the right level for a general audience (link). It uses the 3M Cloud Library application.
The Digital Reader provides an overview of comparable platforms (link).
Polaris is yet commercial library platform (link).
biblibre.com are a consulting group that provide open source services to libraries (link).