\newcount\y \newcount\x \newcount\i \newcount\j
\def\alphabetshow{\y=`a \i=1
  \vbox{\offinterlineskip%
    \loop\ifnum\i<27
      \x=\y \j=1
      \hbox{\loop\ifnum\j<27
          \ifnum\x>122 \advance\x by-26 \fi% 
          \hbox to.55em{\hss\char\x\hss}\advance\x by1 \advance\j by1% 
        \repeat\hss}
      \advance\y by1 \advance\i by1
    \repeat
  }
}

$$\alphabetshow$$