Featured live in geocar's presentation: https://www.youtube.com/watch?v=kTrOg19gzP4&list=PLmRrx948XM...
Also: - "Arthur wrote an SQL in 20 lines of K, and a dynamic window manager in around 60 of C...kOS's kernel is under 60 lines of C as well (including annotations; paging, filesystem, syscalls, etc)." (https://news.ycombinator.com/item?id=9002302)
- "k includes language, files, procs, ipc, webserver, dbms, ..z includes graphics...edit.k is 1KB code + k/ztk(9KB)." (http://kparc.com/o.htm)
- "kOS doesn't use the Linux kernel code. It supports a few of the same syscalls: clone, execve(!), epoll_create, epoll_ctl, epoll_wait, dup2, stat, rename, unlink, getcwd, chdir, fstat, getdents, open, close, read, write, ftruncate, mmap2, munmap, ioctl, gettimeofday, socket, bind, connect, listen, acccept, socketpair, setsockopt...execve just runs another k interpreter (regardless of what you tell it to do) though, so it can just be used to run more k programs." (https://news.ycombinator.com/item?id=8744769)