That can be achieve in plain LaTeX without any specific package.
\documentclass{article}
\begin{document}
This is your only binary choices
\begin{math}
\left\{
\begin{array}{l}
0\\
1
\end{array}
\right.
\end{math}
\end{document}
This code produces something which looks what you seems to need.
The same example as in the @Tombart can be obtained with similar code.
\documentclass{article}
\begin{document}
\begin{math}
f(x)=\left\{
\begin{array}{ll}
1, & \mbox{if $x<0$}.\\
0, & \mbox{otherwise}.
\end{array}
\right.
\end{math}
\end{document}
This code produces very similar results.
