RPi-Buildroot is a fork of Buildroot, you can use it to build a customized system for your next embedded project. Just be sure to be familiar with Buildroot itself and how cross-compilation works.
Build a trimmed down, fast custom Linux distro for your next Raspberry Pi project.
Honestly, the whole idea of forking a sprawling and fast-moving project like buildroot is pretty insane and thus this project is unmaintained. Buildroot has better facilities for extending their capabilities without having to fork the whole darn thing -- see https://buildroot.org/downloads/manual/manual.html#outside-br-custom
For anyone looking to run buildroot on Raspberry Pis, just use stock buildroot, they have maintained, very minimal Pi based defconfigs. Currently:
raspberrypi0_defconfig
raspberrypi0w_defconfig
raspberrypi2_defconfig
raspberrypi3_64_defconfig
raspberrypi3_defconfig
raspberrypi3_qt5we_defconfig
raspberrypi4_64_defconfig
raspberrypi4_defconfig
raspberrypicm4io_64_defconfig
raspberrypicm4io_defconfig
raspberrypi_defconfig
raspberrypizero2w_defconfig