OpenBudgets.eu will provide an open-source software framework and accompanying Software-As-A-Service (SAAS) platform for supporting financial transparency, thus enhancing accountability within public sectors, and as a result preventing corruption. The core objectives of OpenBudgets.eu project are: a semantic data model; a library of visualisation tools with a user-friendly interface; a library of data mining and comparative analysis tools; a feedback and citizen engagement interface. The OpenBudgets.eu open-source framework and portal will integrate these components into a comprehensive portal. The framework will be deployed as a software-as-a service for thousands of public administrations and millions of citizens. We will apply the project concept to three large-scale pilot scenarios in the domains participatory budgeting, data journalism and corruption prevention.