the gnu/linux world supports various cluster software; for application clustering, there is distcc, and mpich. linux virtual server, linux-ha - director-based clusters that allow incoming requests for services to be distributed across multiple cluster nodes. mosix, linuxpmi, kerrighed, openssi are full-blown clusters integrated into the kernel that provide for automatic process migration among homogeneous nodes. openssi, openmosix and kerrighed are single-system image implementations.