eCos stands for embedded Configurable OS. It was begun by Cygnus. Then Red Hat, Inc., bought Cygnus and merged it into Red Hat. Now, eCosCentric Ltd. (UK), manages eCos. It is a royalty free, open source RTOS for embedded systems, and 50% of the RTOS market using in-house developed kernels. Highly configurable almost down to subroutine level: application-specific. All aspects of kernel configurable: over 300 possible configuration parameters. POSIX and Japanese uITRON compatibility layers, TCP/IP, PPP, SNMP, filesystems, and more. Full architecture simulator of many semiconductor firm evaluation boards.