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Invision - Prototyping and collaboration for design teams
Sitemod - Modify any website in real-time. Share it with the world.
Zeplin - Collaboration app for UI designers & frontend developers
Sidemail - The simplest way to send transactional emails. Sidemail makes sending transactional emails trivial, it's perfect for side projects, MVPs or the next big thing.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.