I recently had to setup a simple, straightforward file server.
I chose to install the Turnkey File Server Appliance as it had everything I wanted, ready to use.
Following a SAMBA tutorial I could set the server so Samba users can have access to shared resources.
However, for a public share I wanted to have a completely anonymous access, without any authentication prompt.
I found the answer here, the key is to add
map to guest = bad user
In the global section of /etc/samba/smb.conf