IncludeOS

IncludeOS is a minimal, open source, unikernel operating system for cloud services and IoT. IncludeOS allows users to run C++ applications in the cloud without an operating system. IncludeOS adds operating system functionality to an application allowing oneself to create a 'virtual machine' for an application.
IncludeOS applications boot in tens of milliseconds and require only a few megabytes of disk and memory.
Architecture.
The minimalist architecture of IncludeOS means that it does not have any virtual memory space. In turn, therefore, there is no concept of system calls nor user space.