Because it’s the most common masculine singular nominative suffix, Greek is full of nouns and adjectives that end in “-os” (“-ος”), including many people’s names, although in many cases English got them by way of Latin, which usually substituted its own masculine singular nominative suffix, “-us”. And there’s also an “-ιος” suffix (I think that’s the singular genitive of the same declension?) which gives us names like “Apollonios” and “Dionysios” and Hephaestus's epithet “Aitnaios”, as well as highly productive suffixes like “-ασσος”, for places, and “-ισμος”, for procedures or beliefs. Of course, to a programmer, the “-os” suffix sounds like an operating system, like MacOS, AmigaOS, MS-DOS, RISC OS, iOS, IOS, BeOS, GEOS, GECOS, SunOS, Unicos, ReactOS, FreeDOS, TempleOS, KeyKOS, Palm OS, ChibiOS, and the like, and there is a long tradition of naming computer systems after figures from Greek mythology, such as Kerberos and Project Athena.
So multilingual puns seem to be called for.
This is not an entirely new idea; CDC named an OS “Kronos”, there was an MS-DOS alternative called “THEOS”, of course EROS, and there has probably been more than one OS called Cosmos, DEMOS/ДЕМОС, and at least three named Minos.
Adding to the potential for multilingual puns, masculine plurals of nouns and adjectives in Spanish and Portuguese also commonly end in “-os”, and “Unicos” and “AROS” are already Spanish (and Portuguese) words, meaning “only” and “rings/earrings” respectively; Liddell and Scott additionally define ἄρος as “use, profit, help”. Too bad it’s already taken!
But we could imagine, for example, the cult of HefaistOS AitnaiOS in LemnOS, OdysseOS, DionysOS and his thiasOS and SeilenOS drinking from a cantharOS, carrying a thyrsOS (with which fire was stolen) and suffering a sparagmOS, hermaphroditOS, FalOS, OceanOS, TyrnavOS, PriapOS, GlaucOS, LycurgOS, ScyrOS, KotylOS, AscOS, AryballOS, CyprOS, TheofrastOS, DiodorOS Siceliotes, HerodotOS, FlaviOS PorfyrogenitOS, HalicarnassOS, HomerOS, ChiOS, ChaOS, EustachiOS, DemetriOS, ParnassOS, PeisistratOS, SamOS, LogOS, StrategOS, HyperbolOS, PeloponnesOS, ArgOS Panoptes, HeliOS, Hermes TrismegistOS, AtreOS, Eos, OrpheOS, TartarOS, BriareOS, AnytOS, IapetOS, OlympOS, ApollodorOS, OuranOS, KratOS, TheOS ProterOS, FolOS, ThespiOS, ErymanthOS, PithOS, PylOS, KnossOS, AngelOS, TyphOS or TyphoiOS, AischylOS, PatroclOS, FaidrOS, OrthOS (which is “assholes” in Spanish, though misspelled), KadmOS, AigyptOS, NarkissOS, IkarOS, TalOS the gift of HefaistOS KholOS to MinOS, KokalOS who gave DaidalOS refuge in KamikOS from MinOS, PegasOS, OrfeOS, AisculapiOS, MinotaurOS, CetOS, AgriOS, EnkeladOS, HippolytOS, SisyphOS, NessOS the son of KentaurOS who slew Herakles the lover of IolaOS and slayer of AntaiOS, AkhaiOS, NostOS, LykourgOS the law-giver, LesbOS, BarbarOS (which in colloquial Argentine Spanish meaning “excellent”), DemosiOS (“public”, of the δημος), HeraklitOS, OstrakismOS, ByblOS, PapyrOS, BybliOS, DiOS (“of Zeus”), and so on.
Several other promising names turn out to not end in “-ος” in Greek: Prometheus and Theseus, for example.
Really, though, you can probably find a Greek name ending in “-ος” for any concept you care to name an OS after.