The FOLK project aims to provide a single patch which incorporates as many Linux kernel projects as can be crammed in. Its goal is to allow people who are interested in experimenting with the different projects to get on with the experimenting, rather than spend time fixing clashing diffs. It also has the goal of giving some of the more obscure projects a better chance of being seen and used. It is not intended for "general use". If a given release is stable, that will be by sheer luck. These are experimental projects, of unknown quality and completeness, being thrown together in ways that the developers are unlikely to have even remotely considered.
openMosix is a a set of extensions to the standard Linux kernel allowing you to build a cluster of out of off-the-shelf PC hardware. openMosix scales perfectly up to thousands of nodes. You do not need to modify your applications to benefit from your cluster (unlike PVM, MPI, Linda, etc.). Processes in openMosix migrate transparently between nodes and the cluster will always auto-balance.
chpox provides transparent checkpointing and restarting of processes on Linux clusters. It was originally designed for recovering tasks that have a long execution time (i.e. numerical simulations) in case of system crashes, power failures, etc. It may work with openMosix, is SMP safe, does not require program recompiling/relinking, and supports virtual memory, regular open files, pipes, Unix domain sockets, current directory, and child processes.
Kerrighed is a Single System Image operating system (SSI) for clusters. It offers the view of a unique SMP machine on top of a cluster of standard PCs. The goals are high performance of applications, high availability of the cluster, efficient resource management, high customizability of the operating system, and ease of use. It is implemented as an extension to Linux operating system (a set of Linux modules and a small patch to the kernel).