\documentclass{article}

\usepackage{mkessler-mathfont}
\DeclareMathAlphabet{\mathpzc}{OT1}{pzc}{m}{it}

\begin{document}
cal com cat frak scr
\def\letters{ABCDEFGHIJKLMNOPQRSTUXWXYZ}
    \[
        \mathcal{A} \mathcat{A} \mathfrak{A} \mathscr{A}
    \]
    mathcalo
    \[
        \expandafter\mathcalo\expandafter{\letters}
    \] 
    mathcal
    \[
        \expandafter\mathcal\expandafter{\letters}
    \] 
    neue kalligraphie
    \[
        \expandafter\mathpzc\expandafter{\letters} ABC
    \] 
    mathscr
    \[
        \expandafter\mathscr\expandafter{\letters}
    \] 
    mathfrak
    \[
        \expandafter\mathfrak\expandafter{\letters}\mathfrak{p}\mathfrak{q}
    \] 
\end{document}