The Mundaneum was an institution created in 1910, following an initiative begun in 1895 by Belgian lawyers Paul Otlet and Henri La Fontaine, as part of their work on documentation science. It aimed to gather together all the world's knowledge and classify it according to a system they developed called the Universal Decimal Classification. Otlet and La Fontaine organized an International Conference of International Associations which was the origin of the Union of International Associations (UIA).
The English language version of the Mundaneum Museum website is 
More information on the Wikipedia page