Open Source Portfolio (OSP) is a set of integrated tools that live inside the full Sakai Collaboration and Learning Environment (Sakai describes itself as a "Collaboration and Learning Environment" (CLE). A CLE is an environment where professors can prepare and deliver courses, communicate, and collaborate with their students, It can also support ad hoc group collaboration, electronic portfolios, and research collaboration. In education, the most common term to describe the teaching and learning part of this tool set is "Learning Management System" (LMS).">CLE).
OSP and Sakai are both community source projects of the non-profit Sakai Foundation.
See the FAQ: Can I use OSP without using Sakai?