A microkernel, preemptive multitasking, symmetric multiprocessing, object-oriented, real-time OS for Pentium and PowerPC developed by Jean-Louis Gassée, an ex-Apple man. The BeOS is based on a concept called the Media OS. Similar to  NeXTstep. Available for Mac, soon for  PC. Has  OO database as filesystem. The first OS that handled multiprocessors well. Adheres to Posix. Originally launched in late 1990. 

BeBox had dual Motorola chips. After hardware was discontinued, BeOS was ported to Macs, then to Intel just in time before the G3 chip came out, because Apple withheld the data on it that the Be engineers would have needed to make BeOS run on the G23. 

Is European and made a stronghold in Japan. Hitachi ships PCs with Be pre-installed (1999).  

(  The company was bought up by Intel. Be hardware has been discontinued. Will fill a niche left vacant by the Amiga: video, 3D, small fast applications.) 
 
Release 4 has arived at our resellers and it is now possible to get the BeOS with a French or German Manual. 

Beowulf  
parallel OS for  Linux Cluster. 

SMILE (Scalable Multicomputer Implementation using Low-cost Equipment) 
 

BSD Unix 
The University of California at Berkeley (UCB) deserves special mention, because their Computer Science Research Group (CSRG) developed the BSD (Berkeley Software Distribution) variants of AT&T's UNIX operating system. 
     Based on Unix Version 7 / System III (?), enhanced by virtuell System (for DECs VAX ) bo. kernel-enhancements, Fast File System, Sockets for TCP/IP and programs as vi by  Bill Joy.
     From1983 on BSD has been ported to some other machines which support virtual memory management, such as SunOS and Ultrix from Digital. UCB doesn't support BSD after BSD4.3 . From version 4.4 free. Has no comercial impact..

- Marshall Kirk McKusick, Twenty Years of Berkeley Unix: From AT&T-Owned to Freely Redistributable, in: Open Sources: Voices from the Open Source Revolution, O'Reilly & Associates, Inc. 1999 

Besides Linux the free BSD-unices are the most promising and used  Os's at the moment.

- FreeBSD  sure worth a visit!
free Unix like Operating System for PC's. Has many ported Applications 

FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. An operating system for a variety of platforms which focuses on features, speed, and stability. Freebsd is developed and maintained by a large community. FreeBSD is a 4.4BSD-Lite release and packs enhancements from the Lite2 release. It gives you access to a repository containing a staggering 20,000 packages for various use cases. Currently, at version 12.3, FreeBSD is meant explicitly for computing on i386, amd64, IA-64, ARM, MIPS, PowerPC, ppc64, PC-98, and UltraSPARC platforms. FreeBSD finds its use for embedded platform computing. Ideally, it is also used in networking and server deployment, storage, security, and more.

Wine: On FreeBSD 7.0 and later versions, Wine should work for most user applications. Games tend to be more problematic, but it's worth trying. WineHQ Wine in wikipedia. Wine wikipedia article english.

- NetBSD   sure worth a visit!

- OpenBSD   sure worth a visit!

Wine now successfully compiles on OpenBSD.

DragonFly BSD is an OS based on Unix source and API code. The distro floated to prominence with its standout features, including the HAMMER filesystem, which supports in-built mirroring and historic accessibility.

 GhostBSD Users searching for a more user-friendly Unix-based OS should feel right at home with GhostBSD. The distro is built and powered by FreeBSD, and it incorporates some excellent components from the now-defunct TrueOS.

MidnightBSD features a ready-to-use desktop with open-source software like X.org and GCC, published under GNU step licenses. The familiar Xfce default environment and application setup allow BSD newcomers to dive into the OS for immediate use.

NomadBSD is a live, portable Unix-like distro that you can install on flash drives and use repetitively for system repair and data recovery. This not only applies to Unix and Linux systems but to Windows and macOS as well. The FreeBSD-based codebase allows NomadBSD to immediately detect hardware as soon as you plug it in. You can readily use it for software testing as well.

Download: NomadBSD here

  BSD/OS (Berkeley Software Design, Inc.) COMERCIAL
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.

BS2000 (Siemens)  COMERCIAL(outdated)
ca. 1965 
BS2000/OSD 
 

All about OSs