NetBSD is a free, secure, and highly portable Unix-like Open Source operating system available for many platforms, from large-scale server systems to powerful desktop systems to handheld and embedded devices. Its clean design and advanced features make it excellent in both production and research environments, and the source code is freely available under a business-friendly license.
FreeBSD is an advanced operating system for x86 compatible (including Pentium® and Athlon™), amd64 compatible (including Opteron™, Athlon™64, and EM64T), ARM, IA-64, PC-98 and UltraSPARC® architectures. It is derived from BSD, the version of UNIX® developed at the University of California, Berkeley.
Gentoo is a source-based, free operating system based on either Linux or FreeBSD that can be automatically optimized and customized for just about any application or need. Extreme configurability, performance and a top-notch user and developer community are all hallmarks of the Gentoo experience.
The LiMo is another mobile Linux platform aimed primarily at handsets. It’s development and maintenance is spear-headed by the LiMo Foundation. It’s stated goal is “to create an open, Linux-based software platform for use by the whole global industry to produce mobile devices through a balanced and transparent contribution process enabling a rich ecosystem of differentiated products, applications, and services [...]