Buildroot: out-of-tree builds
Like the Linux kernel, Buildroot supports building out-of-tree in a very similar way. This could be very useful when you have multiple configurations in the same Buildroot repository that you want to build without interference.
Consider the following example:
cd buildroot/
mkdir -p ../outputs/device{1,2}
make O=../outputs/device1 menuconfig
make O=../outputs/device1
make O=../outputs/device2 menuconfig
make O=../outputs/device2
Each output has its own .config so you may change the build configurations independently.
The big benefit compared with git worktree [1] or other multiple-instances-of-the-same-repository-approaches is that the dl directory is shared (without need to specify BR2_DL_DIR [2]) among all build directories.
The feature is documented in the Buildroot manual [3].