Embeddable Linux Kernel Subset

The Embeddable Linux Kernel Subset (ELKS), formerly known as Linux-8086, is a Linux-like operating system kernel. It is a subset of the Linux kernel, intended for "16-bit" computers with limited processor and memory resources such as machines powered by Intel 8086 and compatible microprocessors not supported by "32-bit" Linux.
Features and compatibility.
ELKS is free software and available under the GNU General Public License (GPL). It can work with early "16-bit" and many "32-bit" x86 (8088, 8086) computers like IBM PC compatible systems, and later x86 models in real mode. Another useful area are single board microcomputers, intended as educational tools for "homebrew" projects (hardware hacking), as well as embedded controller systems (e.g. Automation).
Early versions of ELKS also ran on "Psion 3a" and "3aR" "SIBO" (SIxteen Bit Organiser) PDAs with NEC V30 CPUs, providing another possible field of operation (gadget hardware), if ported to such a platform. This effort was called "ELKSibo". Due to lack of interest, SIBO support was removed from version 0.4.0. 
Native ELKS programs may run emulated with "Elksemu", allowing 8086 code to be used under Linux-i386. An effort to provide ELKS with an Eiffel compliant library also exists.
History.
Development of "Linux-8086" started in 1995 by Linux kernel developers Alan Cox and Chad Page as a fork of the standard Linux. By early 1996 the project was renamed "ELKS" (Embeddable Linux Kernel Subset), and in 1997 the first website "www.elks.ecs.soton.ac.uk/" (offline, ) was created. ELKS version 0.0.63 followed on August 8 that same year. On June 22, 1999, ELKS release 0.0.77 was available, the first version able to run a graphical user interface (the Nano-X Window System). On July 21, ELKS booted on a Psion PDA with SIBO architecture. ELKS 0.0.82 came out on January 10, 2000. By including the SIBO port, it became the first official version running on other computer hardware than the original 8086 base. On March 3 that year, the project was registered on SourceForge, the new website being "elks.sourceforge.net".
On January 6, 2001, Cox declared ELKS "basically dead". Nonetheless, release 0.0.84 came along on June 17, 2001, Charilaos (Harry) Kalogirou added TCP/IP networking support seven days later, and in the same year ELKS reached 0.0.90 on November 17. On April 20, 2002, Kalogirou added memory management with disk swapping capability, followed nine days later by ELKS release 0.1.0, considered the first "beta version". By end of the year, on December 18, the "EDE" (Elks Distribution Edition, a distribution based on the ELKS kernel), itself version 0.0.5, is released. January 6, 2003, brought ELKS 0.1.2, an update to 0.1.3 followed on May 3, 2006, the first official release after a long hiatus in development.
A development into "FlightLinux", a real-time operating system for spacecraft, was planned, but the project it was intended for (UoSAT-12) eventually settled on the "qCF" operating system from Quadron Corporation instead.
Current status and usage.
Since January 2012 ELKS is again under development. The CVS repository was migrated to Git in February 2012, and numerous patches from the Linux-8086 mailing list were committed to the new repository. Version 0.1.4 came out on February 19, 2012, released by Jody Bruchon in memory of Riley Williams, a former co-developer. It included updated floppy disk images, fixing compilation bugs of the previous version and removing unused codes. On May 10, 2012, "BusyELKS" was added to the repository by Jody Bruchon in an attempt to replace stand-alone binaries and to take advantage of shared code (ELKS does not support shared libraries). BusyBox-like binaries attempt to save space with symbolic links, eliminating redundant chunks of code, and are combining separate programs into one bigger binary. On November 14, 2013, project development moved to GitHub. Rudimentary Ethernet and FAT support were added in 2017.
More than 35 developers have contributed to this project since the fork in 1995. As of March 2015, development of the ELKS project was again active, reaching a milestone 1,000 source code commits on March 8, 2015. As of June 2018, many bug fixes and improvements were performed with 583 more commits, leading to the 0.2.1 release. In March 2019, the project completed its transition from the obsolete BCC compiler to the more recent GCC-IA16, and development activity increased as Gregory Haerr took the helm as lead developer. During 2019 and 2020 ELKS moved from a 'bootable, unstable' status to a stable Linux-like system for small machines with Ethernet, TCP/IP, FAT16/32, multiuser serial and many more functions. As ELKS 0.4.0 was released in November 2020, the number of commits had passed 3,000.
Version 0.4.0.
Version 0.4.0 represented a major milestone for ELKS, lifting the system from experimental to useful for non-developers, and included the following major enhancements:
ELKS development continues in 2021, adding (by April 2021) Exomizer-like binary compression and new memory models to the tool chain.