Digital library
A digital library is, like a traditional library, a collection of books and reference materials. Unlike a traditional library, however, the collection of a digital library is, as you would expect, digital, and is usually served over the World Wide Web. Some of the largest and most successful digital libraries are Project Gutenberg and iBiblio.
Digital libraries are hampered by copyright law, because works cannot be shared over different periods of time in the manner of a traditional library. The content is, in many cases, public domain or self generated content only. Some digital libraries, such as Project Gutenberg, work to digitize out of copyright works and make them freely available to the public.
External resources:
Google Directory 'Digital Library Development' category]