wxWidgets - wxWidgets: Cross-Platform GUI Library
AskNicely - Collect customer experience feedback on a daily basis and empower your team to take immediate action to drive retention, upgrades, reviews and referrals.
Electron - Build cross platform desktop apps with web technologies
Delighted - The fastest and easiest way to gather actionable feedback from your customers
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Survicate - Collect feedback on your website and find out more about your visitors.