documentclass{article}
usepackage[a4paper]{geometry}
usepackage[utf8]{inputenc} usepackage[T1]{fontenc}
usepackage{pgfgantt}       usepackage{pgfcalendar}

newcountstartdate
newcountdaynum
pgfcalendardatetojulian{2012-01-09}{startdate}
%Redefinition from pgfcalendar.code.tex
defpgfcalendarweekdayveryshortname#1{%
  translate{ifcase#1Mor Tor Wor Tor For Sor Sfi}%
}
protecteddefzzz{% Mod from http://tex.stackexchange.com/q/87550/19384
pgfcalendarjuliantodate{numexprstartdaterelax}{year}{month}{day}%
pgfcalendarjuliantoweekdaystartdatedaynum
{ifnumdaynum=6color{red}%
tinypgfcalendarweekdayveryshortname{daynum}%
else
tinypgfcalendarweekdayveryshortname{daynum}%
fi}%
globaladvancestartdate1}

begin{document}
noindentresizebox{textwidth}{!}{
  begin{tikzpicture}
    begin{ganttchart}[vgrid={*5{black,dotted},*2{red,dashed}},hgrid,%
                       y unit chart=5mm,x unit=3mm]{20}
      gantttitle{Plan}{20} \
      gantttitlelist[
         title list options={var=y,evaluate=y  as x using
         "{zzz}"}
          ]{1,...,20}{1} \
      ganttbar{Task 1}{2}{5} \
      ganttlinkedbar{Task 2}{6}{8} \
      ganttlinkedmilestone{Goal}{9}\
    end{ganttchart}
  end{tikzpicture}
}
end{document}

documentclass{standalone}
%usepackage[a4paper]{geometry}
usepackage[utf8]{inputenc} usepackage[T1]{fontenc}
usepackage{pgfgantt}       usepackage{pgfcalendar}

newcountstartdate
newcountdaynum
pgfcalendardatetojulian{2012-01-09}{startdate}
%Redefinition from pgfcalendar.code.tex
defpgfcalendarweekdayveryshortname#1{%
  translate{ifcase#1Mor Tor Wor Tor For Sor Sfi}%
}
protecteddefzzz{% Mod from http://tex.stackexchange.com/q/87550/19384
pgfcalendarjuliantodate{numexprstartdaterelax}{year}{month}{day}%
pgfcalendarjuliantoweekdaystartdatedaynum
{ifnumdaynum=6color{red}%
tinypgfcalendarweekdayveryshortname{daynum}%
else
tinypgfcalendarweekdayveryshortname{daynum}%
fi}%
globaladvancestartdate1}

begin{document}
begin{tikzpicture}
begin{ganttchart}[ vgrid = { *5{ black, dotted }%
                            , *1{ red, dashed
                                , double distance between line centers = 3mm
                                , transform canvas = { xshift =  1.5mm } }%
                            , *1{ red!50!white
                                , line width={3mm-0.4pt} % 0.4pt = thin
                                , transform canvas = { xshift = -1.5mm } }%
                            }
                  , hgrid
                  , y unit chart = 5mm
                  , x unit = 3mm
                  ]{1}{20}
  gantttitle{Plan}{20}\
  gantttitlelist[ title list options = { var = y
                                        , evaluate = y as x using "{zzz}" }
                 ]{1,...,20}{1}\
  ganttbar{Task 1}{2}{5}\
  ganttlinkedbar{Task 2}{6}{8}\
  ganttlinkedmilestone{Goal}{9}\
end{ganttchart}
end{tikzpicture}
end{document}