Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
Yes, System Workbench for STM32, as avilable on this site, is totally free for both personal and commercial use, to develop code running on STM32 processors.