Premier suppliers of training for the PRINCE2 ('Projects In Controlled Environments') set of qualifications needed a flexible system to cope with on and offline training products available in a number of countries, each with their own set of offerings. They also wanted to be able to cope with corporate and individual buyers, so the system had to cope with people buying courses for other users.
The system involved a number of integrations with external systems - from single sign-on when an online training course is purchased to sending financial reports to their legacy system via Amazon SQS. Drupal Feeds were implemented to feed in data about available offline training courses, each of which is a Drupal Commerce Product. Great care had to be taken here in case of missing data from feeds and potential issues with connectivity and ended up helping improve Feeds garbage collection as much of the Feeds code was written to cope with Drupal Nodes as opposed to Commerce Products.
IP redirection was implemented so you are presented with a different site depending on which country you visit from, as each country has a different set of products available and localised training centres. The organisation has multiple entities which deal with sets of countries so billing was also customised to cope with this on the back-end.