As others said, Samba works and comes with most Linux distributions. All you have to do is set the file rc.samba to executable so it is ran at system reboot, and configure it with smb.conf. Many Linux distros give you tools that make this easy to do. Otherwise, it is simple to do it yourself.
It is very easy to setup shared files so that people can access them, with or without having to enter a password. The hardest part is figuring out how to configure smb.conf. This is an example that lets everyone have read/write access to your /home/SharedFiles directory:
# This one is useful for people to share files
[MyLinuxSharedDrive]
comment = shared file space
path = /home/SharedFiles
read only = no
guest ok = yes
force user = sharedfiles
This gives everyone access to the /home/SharedFiles directory with access level equivalent to the user sharedfiles.
If you don't understand what I've said, find someone that understands filesharing with Linux to help you set it up, or see if your distro had some built in tools to set it up for you.
Google samba for more information on getting samba working for you.