Invision - Prototyping and collaboration for design teams
Red Pen - Red Pen lets you upload your design, share a short URL, and get live, annotated feedback super-fast.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Notable App - The Markdown-based note-taking app that doesn't suck.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Pixelapse - Visual version control and collaboration workflow for open source and private design projects.