Over the last few years, radio astronomy has undergone a revolution: complex analogue machinery such as dishes is increasingly being replaced by arrays of simple antennae combined with fast networking and high-performance computing. The AARTFAAC project is taking advantage of this to build a round-the-clock monitor of the visible sky, providing a groundbreaking capability to detect to some of the most exciting and energetic astronomical events as they happen. However, turning the signals recorded by the telescope's antennae into astronomically relevant images is highly computationally intensive, and requires the development of a fast, flexible, scalable streaming data processing pipeline. I will describe the design of this pipeline, explaining how we use open source software to address some of the challenges we face and push forward our understanding of the Universe.