Open source tools have recently reached a level of maturity which makes them suitable for building large-scale real-world systems. At the same time, the field of machine learning has developed a large body of powerful learning algorithms for a wide range of applications. Inspired by similar conferences in bioinformatics (BOSC) or statistics (useR), our aim is to build a forum for open source software in machine learning. The workshop's ultimate goal is to bring existing and freshly developed toolboxes and algorithmic implementations to people's attention.