Invision - Prototyping and collaboration for design teams
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.