Responsive Viewer - View multiple screen dimensions in one view
Maze - Beautiful & actionable analytics for InVision prototypes
Responsinator - Designed to test responsive websites on different devices.
UXCam - UXCam is the market leader for qualitative app analytics. UXCam provides instant insight into customer behavior in the app through deep analysis of user sessions, events, screen flows, heatmaps, and interactions.
Multi Screen Test - Test your site at different screen resolutions & devices.
Koncept - Usability testing, interactive prototypes & metrics