musl is a new implementation of the standard library for Linux-based systems. It is lightweight, fast, simple, free, and strives to be correct in the sense of standards-conformance and safety. It includes a wrapper for building programs against musl in place of the system standard library (e.g. glibc), making it possible to immediately evaluate the library and build compact statically linked binaries with it.
HelenOS is a microkernel-based multiserver operating system designed from scratch. By decomposing the operating system functionality into tens of isolated but intensively communicating userspace servers, it provides a computing environment that has several virtues such as flexibility, increased robustness, well defined explicit interfaces, and smaller complexity of individual components. HelenOS does not aim to be another clone of Unix or some other legacy system and is not POSIX-compliant (even though it may seem POSIX-similar at times). Instead, the goal has been to design it according to what is the most elegant and right thing to do. What makes HelenOS unique among the other multiserver operating systems is its multiplatform and multiprocessor microkernel. It will run on seven different processor architectures ranging from a 32-bit uniprocessor little-endian ARMv4 to a 64-bit multicore big-endian UltraSPARC T1.
UNIXem is a small and simple library that provides emulation of several popular Unix API functions on the Win32 platform. Its primary purpose is to assist Win32 programmers who are porting to Unix or are writing multi-platform code. API functions include opendir/readdir/closedir, glob/globfree, readv/writev, pathconf/realpath, mmap/munmap/msync, dlopen/dlclose/dlsym/dlerror, gettimeofday, and getpagesize.
uClibc (µClibc) is a C library for developing embedded Linux systems. It is much smaller then the GNU C Library, but nearly all applications supported by glibc also work perfectly with uClibc. Porting applications from glibc to uClibc typically involves just recompiling the source code. uClibc even supports shared libraries and threading. It currently runs on standard Linux and MMU-less Linux (also known as µClinux) systems with support for ARM, i386, h8300, m68k, MIPS, mipsel, PowerPC, SH, SPARC, and v850 processors.
Facter is a simple cross-platform library for determining basic facts about an operating system, like the operating system name, IP address, or MAC address. It supports multiple mechanisms for resolving a given fact, and these mechanisms can be restricted to only working on specified operating systems or operating system releases.
Curie is a very minimalistic, tiny C library. It supports basic I/O, basic networking, S-expression based I/O, signal handling, process handling, and I/O multiplexing. If the target architecture is explicitly supported, statically linked binaries may be as small as 4-20 kilobytes; if not, then it only relies on the host's C library. The library explicitly does not provide a POSIX interface so that it may be used in conjunction with a regular host libc (or without one).
TurnKey Ruby on Rails Appliance is a server appliance for the Ruby on Rails Web development framework. It is designed to be easy to use and easy to maintain. Security patches are automatically installed. It provides a Web management interface, configuration console, and an AJAX Web shell. To minimize footprint the appliance is built from the ground up with the minimum required components. It runs everywhere thanks to multiple build formats, including an installable live CD, a VMDK with OVF support, and an Amazon EC2 AMI.