Invision - Prototyping and collaboration for design teams
ProjectHuddle - Get design feedback and client approval using WordPress.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Specfox - A free platform for creating beautiful website and mobile app specification documents for your team. No more word templates!
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Red Pen - Red Pen lets you upload your design, share a short URL, and get live, annotated feedback super-fast.