If a "shared diary" is simply something like a word processor or text file, sure. If you want to share it with Windows computers, you need to set up Samba and place the diary in the shared folder. (Tools to set up Samba vary by distribution, and I haven't used Fedora, so look in your distro's help guide.) If the other computers are Linux, share the folder that the diary is in via NFS. Then edit the /etc/fstab of the computers that you want to read/write the diary so that they mount the NFS share at bootup.