claim-dir, claim-mem-dir: userv gadget for claiming directories.

Suppose there's a part of the filesystem namespace that you want users
to be able to claim bits of.  The usual approach is to make the top
directory of the subtree be world-writable and sticky, but this causes
no end of trouble: there's potential contention for the namespace, which
leads to security problems.

These tools provide an alternative approach: a userv service which makes
a directory named after and owned by the calling user, and with
restrictive permissions.  It doesn't set a group for the new directory,
but the caller can do that.