GNOME Builder is fast, clean & simple IDE for GTK application development (on Linux), integrated support for Git and easy possibility to publish the application on FlatHub. This is probably the best IDE for developing applications on Linux
Geany - Lightweight IDE for Linux and Windows
Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...
Visual Studio Code - Build and debug modern web and cloud applications, by Microsoft
Glade - Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit...
wxFormBuilder - wxWidgets is an excellent framework that enables the creation of multi-platform applications with...
Anjuta - Anjuta is a versatile Integrated Development Environment (IDE) for C and C++ on GNU/Linux.