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.
Interactive NPS Calculator (by Delighted) - Calculate your NPS easily with this interactive free tool.
Growth Score - 40+ companies share their Net Promoter Score secrets!
TinyNPS - Simple NPS feedback
Customerville - Net Promoter Scores on steriods
NPS for B2B SaaS - NPS surveys and analytics for B2B teams