wxWidgets - wxWidgets: Cross-Platform GUI Library
GanttPRO - GanttPRO is online Gantt chart software for project management. CEOs, project managers, and teams use it every day to solve project management challenges.
Electron - Build cross platform desktop apps with web technologies
Instagantt - Instagantt is a powerful and intuitive Gantt chart tool to enable teams to plan, manage and visualize their projects easily. Manage your schedules, tasks, timelines, and workload like a Pro. Try it for free.
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
DHTMLX Suite - DHTMLX Suite offers JavaScript UI library for building cross-browser web and mobile applications.