Looping - Fast community feedback on all your designs.
ProjectHuddle - Get design feedback and client approval using WordPress.
Visualtip - A service that allows designers and clients to annotate and collaborate on images in real time
Invision - Prototyping and collaboration for design teams
LimeSurvey - LimeSurvey: the Online-Umfrage Tool - Open-Source Suryeys
Viewflux - Feedback, prototyping and collaboration for designers