documentclass{article}

usepackage[paper=a3paper,margin=1in]{geometry}% Just for this example
usepackage{amsmath,array}

newcommand{BOX}[1][0.125columnwidth]{framebox[#1]}
begin{document}

[
  begin{array}{r@{}>{{}}l@{qquad}r@{}>{{}}l}
    BOX{array} &= BOX{x} & BOX{x}&= BOX{x}\
    BOX{array}&= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
  end{array}
]

begin{align*}
  BOX{align} &= BOX{x} & BOX{x}&= BOX{x}\
  BOX{align}&= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
end{align*}

begin{alignat*}{2}
  BOX{alignat} &= BOX{x} & BOX{x} &= BOX{x}\
  BOX{alignat} &= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
end{alignat*}

begin{flalign*}
  BOX{flalign} &= BOX{x} & BOX{x} &= BOX{x}\
  BOX{flalign} &= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
end{flalign*}

begin{xalignat*}{2}
  BOX{xalignat} &= BOX{x} & BOX{x} &= BOX{x}\
  BOX{xalignat} &= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
end{xalignat*}

begin{xxalignat}{2}
  BOX{xxalignat} &= BOX{x} & BOX{x} &= BOX{x}\
  BOX{xxalignat} &= BOX[0.1columnwidth]{x} & BOX[0.1columnwidth]{x} &= BOX[0.1columnwidth]{x}
end{xxalignat}

begin{gather*}
  BOX{gather} = BOX{x}\
  BOX{gather} = BOX[0.1columnwidth]{x}
end{gather*}

[
  begin{gathered}[t]
    BOX{gathered[t]} = BOX{x}\
    BOX{gathered[t]} = BOX[0.1columnwidth]{x}
  end{gathered}
  quadrule{1em}{.4pt}quad
  begin{gathered}[c]
    BOX{gathered[c]} = BOX{x}\
    BOX{gathered[c]} = BOX[0.1columnwidth]{x}
  end{gathered}
  quadrule{1em}{.4pt}quad
  begin{gathered}[b]
    BOX{gathered[b]} = BOX{x}\
    BOX{gathered[b]} = BOX[0.1columnwidth]{x}
  end{gathered}
]

begin{multline*}
  BOX[0.5columnwidth]{multline start}\
  BOX[0.5columnwidth]{x}\
  BOX[0.5columnwidth]{x}\
  shoveright{BOX[0.5columnwidth]{multline shoved right}}\
  BOX[0.5columnwidth]{x}\
  BOX[0.5columnwidth]{end multline}
end{multline*}

[
begin{split}
  BOX[0.35columnwidth]{split}\
  BOX[0.75columnwidth]{x}\
  BOX[0.65columnwidth]{x}\
  BOX[0.95columnwidth]{x}
end{split}
]

[
begin{split}
   BOX{split} = {}&BOX[0.35columnwidth]{x}\
                   &BOX[0.75columnwidth]{x}\
                   &BOX[0.65columnwidth]{x}\
                   &BOX[0.8columnwidth]{x}
end{split}
]

end{document}