get.realtor is the site I work on for my day job. It is a domain registrar targeting the real estate business. We sell domains in the .realtor® and .realestate top-level domains.
A domain registrar is fundamentally a widely distributed system. The storefront is its own application. Names are registered with the registry. DNS is hosted on dedicated servers. Website and email hosting is usually provided by third parties on their own servers. There is quite a lot to orchestrate, which presents technical callenges on top of the usability challenges inherent in such a technical product.
I have been involved in this project since almost its inception (long before our initial launch). We are a small team, so I have been developer, designer, architect, systems administrator, project manager, and product owner on this project as needed for over five years now.