YesInsights - Get Customer feedback with simple one-click or NPS surveys
Product Fit - Measure product/market fit in app with your users.
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.
Viable Fit - Measure and improve your product market fit
TinyNPS - Simple NPS feedback
NPS for B2B SaaS - NPS surveys and analytics for B2B teams