From the English Wikipedia page [1] - there being more information on the Arabic[2] and Turkish [3] Wikipedia pages.
The Ottoman Archives is a collection of historical sources related to the Ottoman Empire and a total of 39 nations whose territories one time or the other were part of this Empire, including 19 nations in the Middle East, 11 in the EU and Balkan, 3 in the Caucasus, 2 in Central Asia, Cyprus, as well as Israel and Turkey.
The main collection, in the Başbakanlık Osmanlı Arşivleri ("Office of the Prime Minister Ottoman Archives") in Istanbul, holds the central State archives (Devlet arşivleri). These archives are open to scholars, regardless of nationality or research subject.
The Ottoman Archives not only contain information about the Ottoman dynasty and Ottoman State, but also about each nation that holds part of these resources.
The website, in Turkish, is [4]