I use Linux (Mint, Ubuntu, Xbuntu, Lubntu, Kubuntu, Edubuntu, Ultimate Edditon, Linux Mint DE, Mint DPP, Pepper MInt, Manjavo, Fendora, Open Suse, Hannah Montana, Commodore OS Visson, Zevon OS, Zorin OS, Andorid X86, Rebeca Black, Longhorn Linux, and a few more), BSD (PC-BSD, FreeBSD, BSD 4.4 Lite, Dreamshell, Pure Darwin, MidnightBSD, and Unixware.), Solaris (Open Solaris and Open Indiana), and a few others.
OpenIndiana:http://openindiana.org/
RISC OS: https://www.riscosopen.org/content/
Free DOS: http://www.freedos.org/