Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
TinyCat - The online catalog and integrated library system for tiny libraries, powered by LibraryThing.
Invision - Prototyping and collaboration for design teams
BiblioteQ - BiblioteQ strives to be a professional cataloging and library management suite. The SRU and Z39.
Zeplin - Collaboration app for UI designers & frontend developers
Invenio - Invenio is a free, open-source software to run a digital library or document repository on the web.