WinDat Opener does convert to invitations in winmail.dat files. Be aware however that there are some restrictions. For example, Outlook can encode more complex appointment recurrence patterns than iCal can deal with. Also, if the attendees use Exchange server email address, Windat Opener has no way to convert these to regular internet "@" type email address. Finally, WinDat Opener can't convert "Time free/Time busy" requests. So, while WinDat Opener can convert the vast majority of basic appointments, it can't convert 100% of what might be in a winmail.dat file.