Paramecium is a simple and flexible (i.e. adaptable and extendable) operating system used to explore the tradeoffs between user processes and kernel boundaries. Services are provided by objects which are named in a per process name space. Each process may change its own name space, which boils down to installing new services, overriding or interposing existing services, etc. Through the use of code signing a user process may put objects into the kernel address space.