Comercial version of   Plan 9. Lucent is a spin-off of Bell Labs. 
Inferno(tm) is a new network operating system and programming environment to deliver content in a rich environment of heterogenous networks, clients and servers. The Inferno system includes the Inferno kernel, the Limbo(tm) programming language, reference APIs that include interfaces for networking and graphics, network protocols, security and authentication, and various toolkits. Inferno was developed by members of the Computing Sciences Research Center of Bell Laboratories, the research devision of Lucent Technologies.

IOCS (Input Output Control System) 
A pre-OS, like IBSYS for the IBM 7094.  The founding generation of computers had no operating system. The earliest OS- like software in the late fifties were called IOCS (Input/Output Control System) or Monitor. Their main task was to ease Input/Output, not to handle it in the sense of an OS. The OS/360 developed by IBM in 1962 is generally considered the first "real" OS.

ISIS(outdated)

ISIS was the OS delivered with the INTEL(and Siemens second source)-developpement-system for the 8008 and 8080-System in the mid to late 70'ths and early 80ths(at the same time as CP/M). The file system of ISIS used (in the 80ths!!) a variant of the linked-list, which is in this form absolutely not suited for a disc file system: every block on disc had a header forming the linked-list node, which meant that random acces was by design excluded. Since sequential acces tends to be slow, the OS (and by this the processor) had a bad reputation.

ISO (International Standards Organization) 
Homepage 
  ISO/IEC DIS 11685 Information technology -- IEEE trial-use standard specifications for microprocessor operating systems interfaces (MOSI) ISO/IEC 2382-26:1993 Information technology -- Vocabulary -- Part 26: Open systems interconnection  ISO/IEC TR 14252:1996 Information technology -- Guide to the POSIX Open System Environment (OSE) ISO/IEC DIS 14515-1 Information technology -- Programming languages, their environments and system software interfaces -- Portable Operating System Interface (POSIX) -- Test methods for measuring compliance to POSIX -- Part 1: System interfaces ISO/IEC DIS 14515-2 Information technology -- Test methods for measuring conformance to POSIX -- Part 2: Shell and utilities ISO/IEC DIS 14519 Information technology -- POSIX Ada Language Interfaces -- Binding for System ApplicationProgram Interface (API) -- Realtime Extensions ISO/IEC DIS 15068-2 Information technology -- Portable Operating System Interface (POSIX) System Administration -- Part 2: Software Administration  ISO/IEC DIS 15068-3 Information technology -- Portable Operating System Interface (POSIX) System Administration -- Part 3: User and Group Account Administration ISO/IEC 10040:1998 Information technology -- Open Systems Interconnection -- Systems management overview ISO/IEC 7498-1:1994 Information technology -- Open Systems Interconnection -- Basic Reference Model: The Basic Model  ISO/IEC 9040:1997 Information technology -- Open Systems Interconnection -- Virtual Terminal Basic Class Service ISO/IEC 9545:1994 Information technology -- Open Systems Interconnection -- Application Layer structure ISO/IEC DIS 9594-10 Information technology -- Open Systems Interconnection -- The Directory -- Part 10: Use of  Systems Management for Administration of the Directory  ISO/IEC 9595:1998 Information technology -- Open Systems Interconnection -- Common management information service  ISO/IEC 9646-3:1998 Information technology -- Open Systems Interconnection -- Conformance testing methodology and framework -- Part 3: The Tree and Tabular Combined Notation (TTCN)  ISO/IEC 9804:1998 Information technology -- Open Systems Interconnection -- Service definition for the Commitment, Concurrency and Recovery service element usw. ohne Ende...

ITRON
ITRON (industrial TRON) is a real-time operating system specification for embedded systems. Many products have been developed based on the ITRON specifications. ITRON is a de-fact standard operating system specification in Japan for consumer applications.

ITS 
 the MIT AI Lab operating system  

All about OSs