Shared Calander on PDA’s

Is there anyway to sync a shared calander onto a IPaq without having an exchange server ? I have 5 users with iPaqs and can setup everthing to work fine with the users own email, calander, task etc in Outlook. Is there some kind of third party software available that will allow colaboration with the calander? I have tried using public sharefolder (on trial) but cannot get the shared calander folder to sync with the iPaqs using ActivSync – any help appreciated