A X True Type Font Server.
NOTE: Name of executable is "xfs.xtt", rather than "xfs".
For more info, See
http://cclub.tutcc.tut.ac.jp/%7Ego/unix/xtt.html
or
http://www.ryukyu.ad.jp/%7Eshin/linux/x-tt/
or
http://hawk.ise.chuo-u.ac.jp/student/person/tshiozak/study/
freebsd-at-random/x-tt/index-en.html (in English)
enjoy!