This open access book constitutes the refereed proceedings of the 15th IFIP WG 2.13 International Conference on Open Source Systems, OSS 2019, held in Montreal, Quebec, Canada, in May 2019. The 10 revised full papers and 5 short papers presented were carefully reviewed and selected from 35 submissions. The papers cover a wide range of topics in the field of free/libre open source software (FLOSS) and are organized in the following thematic sections: mining OSS data; organizational aspects of FLOSS projects; FLOSS adoption; FLOSS cost and licenses; and FLOSS education and training.

This book constitutes the proceedings of the 11th European Conference on Modelling Foundations and Applications, ECMFA 2015, held as part of STAF 2015, in L`Aquila, Utaly, in July 2015. The 13 papers presented in this volume were carefully reviewed and selected from 54 submissions. The committee decided to accept 13 papers, 9 papers for the Foundations Track and 4 papers for the Applications Track. Papers on a wide range of MBE aspects were accepted, including topics such as aspect-oriented modeling, model management, model transformation, advanced meta-modeling, UML modeling tools, and domain-specific modeling w.r.t. energy consumption and cloud-based systems.