Vial is an open-source cross-platform (Windows, Linux and Mac) GUI and a QMK fork for configuring your keyboard in real time, similar to VIA.
If you’re already familiar with VIA, the major difference is that Vial is a completely open project, with sources for all components publicly available on GitHub.
Another big goal for this project is to reduce reliance on third parties when developing a new keyboard.
With Vial, you do not have to submit your keyboard as a pull-request for QMK and/or VIA before it can be used in the GUI; rather, the keymap JSON definition is stored within the keyboard firmware and is retrieved at runtime.
Vial implements several additional quality-of-life features that are documented in the topics linked below including support for rotary encoders.