Zephyr's System build (sysbuild) is a high level build system that you can use to combine multiple build systems and build images for one or more boards or domains as part of a single process. Sysbuild is written in CMake, is integrated with west, and comes with its own Kconfig options and configuration namespacing. You can read more about Sysbuild in the Zephyr documentation.
Important
Sysbuild is available in the nRF Connect SDK from the v2.7.0 release.