\frame { \frametitle{What is Cactus for?}
 Assume:
 \begin{itemize}
  \item Computational problem
  \item Too large for single machine
  \begin{itemize}
   \item<2-> \only<5->{\textcolor{cactusgreen}}{OpenMP}
   \item<2-> \only<5->{\textcolor{cactusgreen}}{MPI}
  \end{itemize}
  \item Distributed development
  \begin{itemize}
   \item<3-> \only<5->{\textcolor{cactusgreen}}{Modularize Problem}
   \item<3-> \only<5->{\textcolor{cactusgreen}}{Versioning system(s)}
  \end{itemize}
  \item Multiple programming languages
  \begin{itemize}
   \item<4-> \only<5->{\textcolor{cactusgreen}}{Modularize Problem}
   \item<4-> \only<5->{\textcolor{cactusgreen}}{Interfaces for inter-language communication}
  \end{itemize}
 \end{itemize}
}