The Project Akita OS (Orange OS) was started with the intent to design a lightweight operating system. It contains a small kernel designed for those interested in the low-level, practical aspects of building an x86 system. The host development environment is designed to work around the Bochs x86 emulator, so that you can easily test changes to the kernel.
NASLite is a Network Attached Storage (NAS) server operating system designed to transform a basic computer into a dedicated file server. Utilizing highly optimized versions of Samba, uCLibc, BusyBox, and various other Linux tools, it provides SMB/CIFS, FTP, or NFS filesystem support. It accommodates multiple client OSes: Windows, Mac OS X, and Linux. NASLite offers SMART disk monitoring and large file support, and is incredibly easy to install and administer.