Cagefs is intended to be a protection layer aganist new symlinks by malicious users in case you want to have a system that users can only store files on, not execute commands, and where they need wide symlinks that were created by administrators.
All that cagefs does currently is blocking symlinks. This is how you can use it:

# cagefs -o allow_other,default_permissions /var/symlink_protected/

Nearly the whole code currently comes from the "fusexmp" sample fs from the fuse source.