Incoming Feedback by Hotjar - Instant visual feedback for your website or app!
draw.io - Online diagramming application
Canny - Canny helps you collect and organize feature requests to better understand customer needs and prioritize your roadmap.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
ProductBoard Customer Feedback Portal - Share feature plans and collect feedback at scale for free
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.