MAS (Modula-2 Algebra System) is an experimental computer algebra system (CAS), developed at the University of Passau. MAS combines imperative programming facilities with algebraic specification capabilities for design and study of algebraic algorithms. It contains a large library of implemented Groebner basis algorithms for nearly all algebraic structures where such methods exist. MAS further includes algorithms for real quantifier elimination, parametric real root counting, and for computing in (noncommutative) polynomial rings.