Generally spelled FOSSie. One who uses "Free and Open Source Software" (FOSS).
Common views are that charging money for software is evil, that computer programmers should be modern society's slave labor, and that anything and everything related to Microsoft is evil.
Your common FOSSie will spend all day at Slashdot.org, giving negative moderation to anyone who dares to interject anything rational in the forums.
I don't know how those FOSSies talked the City of Munich into totally converting their IT to Linux-based, but they have been at it since 2002 with no end in sight. People are literally begging for Windows-based sanity at this point.