Martijn, from Holland Winkel wrote a very interesting article about the requirements for a Magento website owner and the solutions to manage inventory, purchasing and order fullfilment.

"We looked at several Open Source ERP packages, but none provided the integrated functionality with Magento that we were looking for. Our preferred option was to have a Magento module that provided inventory management beyond Magento’s basic functionality. When we came across Embedded ERP it immediately sounded like the solution to our problem. Even better — it provided much more than our initial requirements."

Read more on Martjin's Magento blog