This econometric software is used to build and simulate very large econometric models (with hundreds or thousand of equations). Thus, its users include the Federal Reserve, the European Central Bank, the IMF, and many others. It contains more than 300 built-in functions and you can easily add your own. TROLL includes numerous estimation methods, and it can solve rational expectations models using the Fair-Taylor or Stacked-Time algorithms. It can be linked to many different types of databases, can read and write .WKS and .WK1 files, and it can call external C programs. They offer both a command line and GUI interfaces for its many platforms.