Summer projects (preferably open source) for college sophomores

I am the parent of a college sophomore. My son is learning data science in the US. He likes computer algorithms and computer security and is willing to code or contribute otherwise. Please suggest meaningful projects (preferably open source) to do over the summer. He can work on them for about 120 hours.

I ask here because he'd like the form of project to be semi-formal (no remuneration is expected, only fun and challenge are what he's looking for) and also because people here are very knowledgeable.