Non-governmental Organizations (NGO) usually have limited resources that prevent them from investing in software-based innovation. Sometimes hackathons are used as a resource to crowdsource software for NGOs, but often the resulting projects are not usable or not carried on. These events are not seen as a good option in Software Engineering for social good (i.e., software focused on social change) since they are too short to allow understanding the social context of the target institution. Taking that limitation into account, after performing 6 months of ethnography to understand the social context of an NGO, by identifying user needs and eliciting requirements, we organized an inclusive hackathon to address two specific challenges identified in that organization. This papers presents an experience report in the context of an interdisciplinary project with researchers from the Psychology, Design and Computer Science domains, where the goal is to propose and apply an Open Social Innovation process focused on digital innovative solutions in the context of an NGO from [ommitted developing country] that supports socially vulnerable people living with HIV/AIDS.