This document comprises the final report on the IST Integrated Project XtreemOS - "Building and promotinga Linux-based operating systems to support virtual organizations for next generation Grids".The project started in June 2006 and ended in September 2010.The XtreemOS operating system provides for Grids what a traditional operating system offers fora single computer: abstraction from the hardware and secure resource sharing between different users.It thus simplifies the work of users belonging to virtual organizations by giving them the illusion ofusing a traditional computer while removing the burden of complex resource management issues of atypical Grid environment.We have developed a comprehensive set of cooperating system services. Xt...