Latex bracket on multiple lines

This works because stackengine can set equations with fixed baselineskip.

documentclass{article}
usepackage{tabstackengine,amsmath}
TABstackMath
stackMath
begin{document}
[
%setstackgap{L}{1.1baselineskip}% VERTICAL SPACING OF CENTER EQUATIONS
%renewcommandstacktype{L}% GIVES LEFT/RIGHT EQS SAME VERTICAL SPACING AS CENTER EQS
Centerstack{


alignstackanchor{a=&b}{a=&b}{left{begin{aligned}\end{aligned}right.}


alignstackanchor{a=&b}{a=&b}{left{begin{aligned}\end{aligned}right.}

}
alignCenterstack{
a=&b
a=&b
a=&b
a=&b
a=&b
a=&b
a=&b
a=&b
}
Centerstack{
smash{phantom{left.begin{aligned}\end{aligned}right}}}a = b


{left.begin{aligned}\end{aligned}right}}alignstackanchor{a=&b}{a=&b}


{left.begin{aligned}\end{aligned}right}}alignstackanchor{a=&b}{a=&b}
}
]
end{document}

Just a small try, but Steven B. Segletes answer is 100 times better than mine, here is the MWE for my try:

documentclass{book}
usepackage{mathtools,multirow}
begin{document}

begin{tabular}{ccc}
&$begin{matrix}
a=b
a=b
end{matrix}$ &$a=b$
$begin{matrix}
a=b
a=b
end{matrix}$ &multirow{-2}{*}{Bigg{} $begin{matrix}
a=b
a=b
end{matrix}$ &multirow{2}{*}{Bigg}} $begin{matrix}
a=b
a=b
end{matrix}$[19pt]
$begin{matrix}
a=b
a=b
end{matrix}$ &multirow{-2}{*}{Bigg{} $begin{matrix}
a=b
a=b
a=b
a=b
end{matrix}$ &multirow{2}{*}{Bigg}} $begin{matrix}
a=b
a=b
end{matrix}$
end{tabular}

end{document}

A solution with bigdelim:

documentclass{article}
usepackage{amsmath}
usepackage{array, bigdelim} 

begin{document}


[setlength{extrarowheight}{3pt} begin{array}{c@{,}c@{enspace}c }
 & a = b & a = b 
 ldelim{{3}{*}[$ begin{gathered}
 a = b  a = b
end{gathered} $ ] & a = b 
& a = b & rdelim}{3}{*} [$ begin{gathered}
 a = b  a = b
end{gathered} $ ]
  & a = b 
ldelim{{3}{*}[$ begin{gathered}
a = b  a = b
end{gathered} $ ] & a = b 
  & a = b 
  & a = b 
  & a = b 
end{array} ]%

end{document}