Nanos is a microkernel OS running in x86 PC systems Pmode starting at Pentium (although it could easily be modified to run on a 386). The intentions are to create a kernel with as little functions as possible. The rest can be added as drivers such as harddisk, soundcard, monitor, or even disk cache. This way the OS will only have to run that it needs for its task.
Features build in into the kernel are system hardware, memory and multitasking management(preemtive). These are services which must be included to have a running system. Other features are managed as drivers such as display driver and even some drivers very near the OS such as disk cache(or over a network) which needs OS privileges but still isn't neccesary for a running OS.
Protection in Nanos will be with the build in ProtectedMode memory, port and task features. Memory management will use both the paging and the segment mechanism. Some features will be aliasing - allowing two programs access the same memory chunk even if they can't access the rest of each others data.
Nanos is written in assembler using NASM.