I was looking for a list of the tables and fields in SAP B1 and found a great site:
The person that maintains this site also maintains a similar site for the JD Edwards application
So while I was at it I thought I would see if anyone had done something similar for Great Plains. I found a few sites.
This type of information is usually available directly from the vendor, but often those resources are restricted to licensed users with a support account. The sites above are open to the public. If you know of has a similar site for another application, let me know and I will add it here.