The course of lectures included in the brochure introduces the reader to popular free programs and systems useful in teaching computer science in high school. The review included the basics of open operating systems, information about the OpenOffice.org office software package, the Mozilla communication package, the GIMP graphics editor, modern GNOME and KDE graphical environments and other programs. The text of lectures published by the author was used in the supplement to the newspaper “First of September” “Informatics” ( in 2002-3, materials from the brochure “Applied free programs at school” (M.: 2003), as well as fragments articles previously published in Computerra and Home Computer magazines. The materials presented in this book are also available on the Internet at www.otstavnov.com/fsft under the terms of the GNU Free Documentation License (GNU FDL ). All other rights are reserved by the author.