ARC is a project to run Play Store apps on Chrome OS. Each subdirectory contains daemons, helpers and/or tools to run ARC. See README.md in each subdirectory for details.
arc/container/ is for packages that are used only in P (ARC container). arc/vm/ is for packages that are used only in R+ (ARCVM). Packages that are both for P and R+ such as mount-passthrough/ and keymaster/ can live in arc/.