Maiden-core is a Linux kernel robotics API module, extensible in Erc. The Maiden Project also documents and develops the Maiden architecture for mobile robots, a set of (optional) designs and standards for robots using the Maiden-core API.
lysis is working on a features rich home automation system that ranges from CAN-bus, 1-wire and RF up to a HTPC; both hardware and software are addressed to make the really smart home; the domotics will provide energy saving, comfort, flexibility, safety
robot-brains is a repository for diy roboticists and experimenters. It's focused on Scheme.
uGNU/RTOS (literally "micro G'Noo RTOS") is an Open Source serial Real Time OS for microcontrollers (PIC, ATMEL).