\begin{abstract} The Brazilian Public Software (SPB) is a program promoted by the Brazilian Federal Government to foster sharing and collaboration on Free/Libre/Open Source Software (FLOSS) solutions for the public administration. In this context, a public software is considered a public good and the Federal Government assumes some responsibilities related to its use. Once its devolpment principles is the same of the FLOSS projects, we have designed the SPB Portal, a platform based on the integration and evolution of existing FLOSS tools. It provides several modern features for software collaborative development, helping the Brazilian public administration in sharing its solutions. In this paper, we present this integrated software development platform that was developed for the SPB program by a heterogeneous team composed by professors, master students and undergraduate students, as well as by professionals from FLOSS communities. The development of this platform used several FLOSS projects, providing a non-trivial integration among them. This effort has also produced several new features that were contributed back to these projects. Alongside the architectural challenges, we also discuss in this paper our work process, based on agile and free software development practices, and the lessons learned during 30 months of work on the SPB project. \end{abstract} \category{K.6.1}{Project and People Management}{Systems development} \begin{comment} %%%%%%%%%%%%%%% \begin{CCSXML} 10011007.10011074 Software and its engineering~Software creation and management 500 10011007.10011074.10011134 Software and its engineering~Collaboration in software development 500 \end{CCSXML} \ccsdesc[500]{Software and its engineering~Software creation and management} \ccsdesc[500]{Software and its engineering~Collaboration in software development} %%%%%%%%%%%%%%% \end{comment} \keywords{\plainkeywords}