Windows NX on the Enterprise.
Windows NX was the operating system used on the Enterprise. It was known to have stability issues and would crash a fair number of times. It was installed on all of the ship's computers and lavatories, and was a frequent subject of formal complaint reports from the ship's sanitation engineer, Lt. Crooman T. Anonnimis. Phlox distrusted the Windows NX transporter program, MyBeam, and installed an alternate version (OpenTransport) for his own use, against the objections of Captain Jonathan Archer (who had signed a contract, after all). After Phlox's explusion from the ship's airlock, Archer assigned a new, more Windows-friendly ship's doctor and immediately signed up for several consecutive physicals.
Windows NX is released by Fleetosoft. The version currently in use, NX Panorama, has been preceded by 86 prior versions. As of the latest release, version 27 was found to be the most stable and has never been bettered.
Bugs are identified by the crew hourly, mainly due to crew dying in excruciating ways due to coding errors. Errors include being blown out of airlocks, various fatal electrocutions and hot plasma leakages, premature ejaculation of torpedos in their launchers, unfortunate accidents in the decontamination chamber, etc.
On one notable occasion, the Enterprise computers were compromised and hacked into by a pre-civilisation caveman race living on Mung III. Their basic knowledge of the English language being sufficient for the attack to occur insured an advertising malware system installed itself, then proceeded to overwrite the life support and climate control components of Windows NX. This incident cost the lives of twelve crewmembers occupying G spot deck 8.
Bug submissions are made to Fleetosoft back on Earth regularly, unfortunately due to the distances involved, updates are thin on the ground and require a full systems restart upon deployment - breathing apparatus and warm weather clothing is issued for all crewmembers during this procedure.
Plans are afoot to replace it with a derivative of Unix, an antique operating system designed hundreds of years prior, but still in use on a moon colony in one washing machine - its worked for many years.