Invision - Prototyping and collaboration for design teams
EUSurvey - EUSurvey is an online survey-management system built for the creation and publishing of globally accessible forms, such as user satisfaction surveys and public consultations.
Red Pen - Red Pen lets you upload your design, share a short URL, and get live, annotated feedback super-fast.
Google Forms - Simple web forms from Google.
Viewflux - Feedback, prototyping and collaboration for designers
LimeSurvey - LimeSurvey: the Online-Umfrage Tool - Open-Source Suryeys