Red Pen is described as 'Lets you upload your design, share a short URL, and get live, annotated feedback super-fast. It remembers you — there's no logging in, no project management, no bullshit' and is a customer feedback manager in the business & commerce category. There are more than 10 alternatives to Red Pen, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and iPhone apps. The best Red Pen alternative is Notism, which is free. Other great sites and apps similar to Red Pen are zipBoard, SureFeedback, Approval Studio and Wake.
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