The ELKS FAQ which I currently maintain.
Various utility programs I have ported to ELKS, including a subset of the GNU file, and shell utilities, a modified configuarable version of sash with configurable builtin commands, and a ported version of mkfs.minix. Also on this page some bits and pieces of code I found on the net which may be relevant to the project.
Coming soon, a set of documents on the kernel source code for ELKS, including an explanation of the boot process, system calls, and a function reference.