FreeBSD is a Free Software operating system distributed under the 2-clause BSD license. KDE4 builds on FreeBSD, but is still very buggy (if Konsole is all you need, it is fine).
The FreeBSD website has all the information needed (especially the handbook) to install and configure FreeBSD itself. The KDE on FreeBSD website is supposed to be the definitive source of information, but this wiki page will be used to collect compilation hints, debugging tips, etc. Additional information can be found on the FreeBSD KDE4 Wiki.