I'd like to set up shared directory trees where users can do full read-write and execute executables, and create and delete directories, and where all new files and directories created by anyone, including root, automatically are given exactly the same permissions. How is this done?
Perhaps you can just create a group, and set the
/etc/sudoers file and allow creating and deleting in a desired directory.
addgroup guest usermod -a -G guest
in the /etc/sudoers file under group sudo
guest ALL:(ALL) /bin/mkdir
and just make the desired directory writable by giving it a reasonable chmod command.