Fiwix is anoperatingsystem kernelwritten fromscratch, basedon the UNIXarchitectureand fullyfocused onbeing POSIXcompatible. Itis designed anddevelopedmainly as ahobby OS and,since it servesalso foreducationalpurposes, thekernel code iskept as simpleas possible forthe benefit ofreaders orstudents. Itruns on the32-bit x86hardwareplatform and iscompatible witha good base ofexisting GNUapplications.
ReactOS is afree and opensourceoperatingsystem writtenfrom scratch.It'sdesign is basedon Windows inthe same wayLinux is basedon Unix,however ReactOSis not Linux.ReactOS looksand feels likeWindows, isable to yourrun Windowssoftware andyour Windowsdrivers, and isfamiliar forWindows users.
FreeDOS is acomplete, free,DOS-compatibleoperatingsystem that youcan use to playclassic DOSgames, runlegacy businesssoftware, ordevelopembeddedsystems. Anyprogram thatworks on MS-DOSshould also runon FreeDOS. Itdoesn’t costanything todownload anduse FreeDOS.You can alsoshare FreeDOSfor others toenjoy! And youcan view andedit our sourcecode, becauseall FreeDOSprograms aredistributedunder the GNUGeneral PublicLicense or asimilar opensource softwarelicense.
The OpenBSDprojectproduces afree,multi-platform4.4BSD-derivedUNIX-likeoperatingsystem.Emphasizingportability,standardization,coherency,correctness,proactivesecurity andintegratedcryptography.It comes withalmost 9000softwarepackage in itsports,including acustom X11environment(Xenocara),desktopenvironments,web andmultimediaapplications,compilers andprogramminglanguages. Italso harbourstheOpenBSD-maintainedsoftwareprojectsOpenSSH,LibreSSL,OpenIKED,OpenBGPD
Kernel basedpublish-subscribeIPC. Publish-subscribetopics arecreated asdevice nodes,which means thesecurity modelis the same asthat of afilesystem. Since the IPCis kernelbased, you donot need tocreate a daemon(egdbus-daemon) toset uppublish-subscribetopics. Also,fanout is twiceas efficient;using Nsyscalls for Nsubscriberscompared to 2*Nsyscalls for aTCP basedpublish-subscribesystem.
HelenOS is amicrokernel-basedoperatingsystem writtencompletely fromscratch. It isnot UNIX-likeand does notimitate anyother OS. Itruns on 7different CPUarchitectures(IA-32, AMD-64,ARM, MIPS,PowerPC, SPARC,Itanium),supports SMP,networking,USB, sound andhas its ownoriginal GUI.