YesInsights - Get Customer feedback with simple one-click or NPS surveys
Viable Fit - Measure and improve your product market fit
Wootric - Wootric is software that allows apps and websites to take customer satisfaction surveys so that you can properly gauge the popularity and success of your app through the eyes of the people using it. Read more about Wootric.
Startup Growth Roadmap - Get from idea to product market fit
TinyNPS - Simple NPS feedback
Focus Framework - A hands on guide to find product-market fit w/ lean methods