PatientOS - an Open Source (GPL) Healthcare Information System. PatientOS (pronounced Patient-oh-es where O and S stand for Open Source) has been designed from the outset to be a Healthcare Information System (HIS). Healthcare Information System (EHR EMR PMS) for small hospitals and clinics. Scheduling, Orders, Meds, Pharmacy, Clinical Doc, HL7, Billing & more. Broad commercial support. Distributed clinical system written in pure Java with toolset to customize.