MyCars was one of the greatest market shakers I have had the pleasure of working on. The system was designed initially to sell repossessed vehicles provided by the banks. 

This system had to be used by the banks to provision approve transaction while another portion had to facilitate internal staff uploading photos of the assets. The public facing system had to handle high volumes of traffic.

 The initial build was done in .NET 4. The system was later converted to PHP which allowed for a lighter back end framework. 

Each aspect of the system was monolithic in nature.