  This note is based on the plenary talk given by the second author at MACIS
2015, the Sixth International Conference on Mathematical Aspects of Computer
and Information Sciences. Motivated by some of the work done within the
Priority Programme SPP 1489 of the German Research Council DFG, we discuss a
number of current challenges in the development of Open Source computer algebra
systems. The main focus is on algebraic geometry and the system Singular.
