Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
Respondent - Respondent helps you find any target audience in the world for in-person and remote research studies across all research methods including interviews, focus groups, surveys, and more. Respondent works with any research tool you already use.
Invision - Prototyping and collaboration for design teams
Startquestion - Say goodbye to boring surveys and forms.
Zeplin - Collaboration app for UI designers & frontend developers
Qualaroo - Qualaroo makes it easy to survey specific groups of website visitors to gain qualitative information.