+t -- If someone has permissions to write
to the directory, they will only be able to modify entries owned by
themselves. Useful for /tmp and other shared spaces where people should not be able to interfere with each others files.
g+s -- new files and directories created in this directory
will belong to the same group as this directory, rather than the
default group of the user.
Useful in shared directories where access is controlled by group membership
and not all participants have that group as their default group.