sudo is a solution that does not require any changes to the file system, and it is backward compatible to ext2 and other older file systems. The general idea is to create a new user, let’s called that a folder user, to represent the shared folder. For any user who should have write access to the folder, either explicitly allow that user to sudo as the folder user, or give that user the password of the folder user so that he/she may use su to accomplish the same effect.
The main disadvantage of this approach is that it involves the maintenance of another user account in addition to group membership. However, it is backward compatible, and is relatively easy to implement.
We will discuss how to use sudo in another module. For the eager and impatient, read the man pages of sudo and sudoers.