Canny - Canny helps you collect and organize feature requests to better understand customer needs and prioritize your roadmap.
Frill - A better way to collect customer feedback
Feedback Fish - Collect feedback & make your customers happy.
Roadmap - Collision avoidance for projects and people
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.
Spaceli - Turn Google Docs into a knowledge base