Unix or Unix-like Operating Systems

• Amoeba (Vrije Universiteit)
  Amoeba is a powerful micro-kernel-based system that turns a collection of workstations or single-board computers into a transparent distributed system. It has been in use in academia, industry, and government for about 5 years.
• Angel (City University of London)
  Angel is designed as a generic parallel and distributed operating system, although it is currently targeted towards a high-speed network of PCs. This model of computing has the dual advantage of both a cheap initial cost and also a low incremental cost. By treating a network of nodes as a single shared memory machine, using distributed virtual shared memory (DVSM) techniques, we have addressed both the needs for improved performance and provided a more portable and useful platform for our applications.
• BSD/OS (Berkeley Software Design, Inc.)
  BSD/OS is a commercial BSD 4.4-based UNIX operating system for the x86 PC. This is where many of the Berkeley CSRG people went after BSD UNIX research ended at Berkeley. A commercial-quality UNIX implementation with all of the bells and whistles one expects from a modern UNIX system. In some sense, a "let's finally make some money out of all of hard our work" project. Seems fair to me.
• Chorus (Sun Microsystems)
  CHORUS is a family of open micro-kernel-based operating system components to meet advanced distributed computing needs in areas such as telecommunications, internetworking, embedded systems, realtime, "mainframe UNIX", supercomputing and high availability. The CHORUS/MiX multiserver implementations of UNIX allow to dynamically integrate part or all of standard UNIX functionalities and services in the\ above application areas.
• FreeBSD
  FreeBSD is one of several free, monolithic BSD 4.4-lite derivative operating systems. It provides full UNIX support, including networking, X Windows, and almost all other normal UNIX services.
• GLUnix (University of California, Berkeley)
  Group Members: Thomaas Anderson, Doug Ghormley, David Petrou, et al.
  Currently, modern workstation operating systems do not provide support for efficient distributed program execution in an environment shared with sequential applications. The goal of our research is to pool resources in a NOW to provide better performance for both parallel and sequential applications. To realize this goal, the operating system must support gang-scheduling of parallel programs, identify idle resources in the network, allow for process migration to support dynamic load balancing, and provide support for fast inter-process communication.
• HURD (Free Software Foundation GNU Project)
  Related to: Mach
  The HURD is the operating system being developed by the Free Software Foundation as the basis for the GNU Project, which has already produced such well known tools as Emacs and GCC. The Hurd is a personality for the Mach micro-kernel which exports a bevy of services to the application. The Hurd will provide the standard UNIX interface, but should also be much more flexible than standard UNIX.
• Linux
  Group Members: Linus Torvalds and a Cast of Thousands
  Linux is a freely-distributable implementation of UNIX for 80386, 80486 and Pentium machines. It supports a wide range of software, including X Windows, Emacs, TCP/IP networking (including SLIP/PPP/ISDN), and the works. Ports to non-x86 machines such as the Alpha and SPARC also exist. This is one rocking project.
• Lites
  Related to: Mach
  Lites is a 4.4 BSD Lite based server and emulation library that provides free unix functionality to a Mach based system. Lites provides binary compatibility with 4.4 BSD. NetBSD (0.8, 0.9, and 1.0), FreeBSD (1.1.5 and 2.0), 386BSD, UX (4.3BSD) and Linux on the i386 platform. It has also been ported to the pc532, and PA-RISC. Preliminary ports to the R3000 and Alpha processors have also been made.
• Lynx (Lynx Real-time Systems)
  LynxOS is a proprietary UNIX-like real-time operating system. LynxOS looks and feels like UNIX from the user/programmer point of view. It was developed from the ground-up with high performance, deterministic hard real-time response in mind. Although LynxOS is conformant with POSIX 1003.1 it is not derived from any AT&T/USL/Novell source code. The OS is in effect a complete re-implementation of UNIX from a real-time perspective.
• Mach-US (Carnegie Mellon University)
  Related to: Mach
  The Mach-US system is an OS developed as part of the CMU MACH project. It is comprised of a set of servers, each of which supports orthogonal system services. For example, instead of one server supplying all of the system services as under the Mach BSD4.3 single server (UX), the Mach Multiserver (Mach-US) has several servers: a task server, a file server, a tty server, an authentication server, a network server, etc. It also has and emulation library that is mapped dynamically into each user process, and uses the system servers to support the application programmers interface (API) of the UNIX operating system.
• Maruti (University of Maryland) Group Members
  Maruti is a time-based operating system research project at the University of Maryland. With Maruti 3.0, we are entering a new phase of our project. We have an operating system suitable for field use by a wider range of users, and we are embarking on the integration of our time-based, hard real-time technology with industry standards and more traditional event-based soft- and non-real-time systems.
• MOSIX (Hebrew University, Jerusalem, Israel) Group Members
  A solution to the NOW problem is now available in the form of a multicomputer operating system enhancements, called MOSIX. MOSIX is an enhancement of UNIX which allows users to use the resources of a NOW configuration, without any change to the application level. By using transparent, dynamic process migration algorithms, MOSIX enhances the network services, i.e. NFS, TCP/IP, of UNIX, to the process level, by supporting load balancing and a dynamic work distribution (leveling) in clusters of homogeneous computers.
• NetBSD Group Members
  NetBSD is one of two free, monolithic BSD 4.4-lite derivative operating systems. It provides full UNIX support, including networking, X Windows, and almost all other normal UNIX services. Unlike many other free UNIX implementations, NetBSD has also been ported to a large variety of hardware platforms.
• OpenBSD
  Yet another group pushing a free BSD-Lite derivative. This group splintered off of the NetBSD project, for reasons unclear to me, although I'd guess perhaps becuase NetBSD wasn't pushing out regular releases fast enough, and FreeBSD wasn't supporting non-x86 platforms. The splintering of BSD people has effectively killed any chance of BSD beating Linux, expecially given the good work porting Linux to other platforms.
• OpenSTEP (Apple Computer Corporation)
  Related to: Mach
  Steve Jobs' brain child after Apple, all that is left of NeXT is the remarkably good NeXTSTEP/OPENSTEP Operating System, a mach-based mostly UNIX with a very good user interface and programmer environment. It's now available for the x86 PC, and many people really like it. OpenSTEP may be the basis of the next Mac OS, Rhapsody.
• QNX
  A micro-kernel, distributed, real-time, fault-tolerant, POSIX-certified OS for the x86. QNX adopts the approach of implementing an OS with a 10 Kbyte micro-kernel surrounded by a team of optional processes that provide higher-level OS services. QNX is fully distributed, with all system interfaces network transparent. QNX has successfully been used in tiny ROM-based embedded systems and in several-hundred node distributed systems.
• RTMX O/S
  Group Members: RTMX Incorporated
  RTMX is a commercial, BSD 4.4-derived, real-time system that offers POSIX 1003.4 real-time programming support with user tunability along with the standard UNIX functionality of BSD networking, X windows, and a full C development environment.
• Sprite (University of California, Berkeley)
  Sprite was a UNIX-like distributed operating system developed at Berkeley which ran on a number of different machines, and had a number of interesting features, such as load-balancing, a high-speed, aggressively-caching, distributed file-system, and a fast log-structured local file-system. Research on Sprite per-se come to an end, although various former members of the Sprite group are carrying on aspects of the original Sprite research.
• Sumo (Lancaster University)
  Related to: Chorus
  Over the past few years members of the SUMO team have been designing and implementing a microkernel based system with facilities to support distributed real-time and multimedia applications and ODP based multimedia distributed application platforms. We are interested in both communications and processing support for distributed real-time/ multimedia applications in end systems, and believe that such applications require thread-to-thread real-time support according to user supplied quality of service (QoS) parameters.
• VSTa
  VSTa is an experimental kernel which attempts to blend the design of a micro-kernel with the system organization of Plan 9. The result is a small privileged kernel running user-mode tasks to provide system services such as device drivers, file systems, and name registry. Like Plan 9, each service provides a file system-like interface.