DeLiRiuM is a 32-bit nanokernel hybrid operating system. One of its aims is developing and testing unconventional interfaces between OS and userspace rather than providing yet another ubiquitous POSIX.1-like API. The goal is to do this in a not only in a programmer friendly way, but also without sacrificing modern OS features or performance. Development currently targets IA-32 (x86), the Xen hypervisor, and Unix userspace. The DeLiRiuM kernel is primarily written in ANSI C and x86 assembler (gas).