Sites and apps similar to Custom Tk Builder include Qt, which is open source with a free version. Other options are PyQt, Avalonia UI, CustomTkinter and Qt for Python (PySide). In total there are seven Software Frameworks like Custom Tk Builder for Linux, Mac, Windows, self-hosting and Android.
Qt is a cross-platform application framework that is widely used for developing application software that can be run on various software and hardware platforms with little or no change in the underlying codebase, while having the power and speed of native applications.
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Avalonia is a WPF-inspired cross-platform XAML-based UI framework providing a flexible styling system and supporting a wide range of platforms including: Windows, Linux (desktop & embedded), macOS, Android, iOS and Browser.
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The Qt for Python project aims to provide a complete port of the PySide module to Qt.
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PyUIBuilder is a Drag and Drop GUI builder for Python developers. Developers can quickly generate Python GUIs in frameworks such as tkinter, Customtk and more. It supports many widgets including 3rd party widget library.
