One of our client wanted to offer an application we made for the client as Software as a Service - so other clients could use the software package completely for their own purposes.
Because of the framework technology we opted for when first designing the application, we were quite fast to realise this.
We were able to keep using the existing database and codebase (no branching into two different products);
By applying a 'filter' over all database queries, the database became highly segmented. Hence it is impossible for a whitelabel user to access the other whitelabels data, and every whitelabel can start with a clean and empty application.