Digital National Library of Serbia includes a large number of digitized collections that are continuously enriched with new contents. Some of the collections are Newspapers, Magazines, Books, Handwritten Periodicals, Cyrillic Manuscripts, Audiobooks, Old Printed Books, Photographic documents, Posters and documentary material. Collection of Handwritten Periodicals includes 15 titles that were created in the period from 1874 to 1995. 14 out of 15 titles represent periodicals which has at least one edition that is entirelyhand-written, while the remaining title is address typing – machine typed, yet supplemented by hand to a lesser extent. From these 15 titles, 14 represents periodicals which are at least oneedition hand-printed in its entirety, while the remaining address typing - typed on the machine, but to a lesser extent, supplemented by hand. Collection of cyrillic manuscripts NBS contains digital copies of selected pages from 180 cyrillic manuscripts of the National Library of Serbia. The collection of audiobooks contains pieces of Bora Stankovic, Branislav Nusic, as well as publications from the portal "Great War" in audio format, available to users for direct playback using the embedded player. Collection of old printed books contains a selection of 16 library units, among which are mainly represented edition of Cetinje and the Venetian editions of Bozidar Vicenca Vukovic. The collection of photographic documents contains digital copies of old photos and postcards from the collection of photographic documents of special funds of National Library of Serbia. Collection of posters and documentary material is a set of digital copies of old posters and ephemeral material from the Graphic collection and Collection of documentary material of special funds of National Library of Serbia. This collection contains collection of theater posters which have been printed in the territory of the Kingdom of Serbia and Kingdom of Yugoslavia in the period from the mid-19th century to 1945. The technical backbone of the Digital National Library of Serbia is Serbia Forum, which is based on the principles of electronic encyclopedias, such as Wikipedia. The main part of the system is a tree-structure of pages, which represent collections, subcollections or digital objects themselves. Serbia Forum is a modular system that supports easy creation and installation of new modules with new functionalities. Some of the most important modules are: an electronic book reader, audio player, system metadata of digitized objects, metadata search system and a module that supports the Open Access Interface protocol. In this paper, authors will present the improvement of existing modules, and will feature some of the new functionality of the system.