LiteOS is a real-time operating system (RTOS) from University of Illinois for use in sensor networks. LiteOS is a Unix-like operating system that fits on memory-constrained sensor nodes. This operating system allows users to operate wireless sensor networks like operating Unix, which is easier for people with adequate Unix background. LiteOS provides a familiar programming environment based on Unix, threads, and C. It follows a hybrid programming model that allows both event-driven and thread-driven programming. LiteOS is open source, written in C and runs on the Atmel AVR based MicaZ and IRIS sensor networking platform.