FreeBSD has several source code repositories:
"src" is used for the system sources, including both kernel and userland. It was recently switched from Subversion to git. The official repository is viewable here. A read-only mirror suitable for Summer of Code projects is available on GitHub.
"ports" repository contains the ports tree and related build infrastructure. was recently switched from Subversion to git. The official repository is viewable here. The mirrors are available at GitHub, GitLab, Codeberg.
For Summer of Code, students can fork the appropriate FreeBSD repository on github or other free hosting services as approved by their mentor. Privately hosted repositories are not allowed by the program.