Haiku is described as 'Open-source operating system that specifically targets personal computing. Inspired by the BeOS, Haiku is fast, simple to use, easy to learn and yet very powerful' and is a very popular operating system in the os & utilities category. There are more than 100 alternatives to Haiku for a variety of platforms, including Linux, Self-Hosted, BSD, Windows and Mac apps. The best Haiku alternative is Linux Mint, which is both free and Open Source. Other great apps like Haiku are Ubuntu, Debian, Fedora and Arch Linux.
MINIX is a POSIX-compliant Unix-like operating system based on a tiny microkernel running in kernel mode with the rest of the operating system running as a number of isolated, protected, processes in user mode.
Netherlands
EU
BeeFree OS is inspired from Ubuntu, Windows 7 and Linux Mint. The name is acronym for Beautiful, Effective, Efficient and Freedom.
Neptune is a GNU/Linux Distribution for desktops based fully upon Debian Stable. It ships with a modern KDE Plasma Desktop with its main view on a good looking multimedia system which allows for getting work done.
An open-source OS for exploration, creation, and play. Kano OS is based on the Raspbian OS which itself is based on Debian, a Linux based operating system.
United Kingdom
The siduction distribution is a desktop-oriented operating system and live medium based on the 'unstable' branch of Debian GNU/Linux.
Pentoo is a security-focused livecd based on Gentoo. It's basically a Gentoo install with lots of customized tools, a customized kernel, and much more.
openmamba GNU/Linux is a ready-to-use operating system for netbooks, notebooks, desktop and server personal computers.
ItalyEU
MorphOS is an AmigaOS-like computer operating system. It is a mixed proprietary and open source OS produced for the PowerPC processor based computers.
GermanyEU
Lunar Linux is a source based Linux distribution. It is built entirely by compiling source code, using custom optimizations.
Brazil
SELKS, a product of Stamus Networks, is a Debian-based live distribution designed for network security management. It provides a complete and ready-to-use Suricata IDS/IPS ecosystem with its own graphic rule manager.
United States
