Since 2011 I work at INDECA GmbH as a Sitecore developer starting with Sitecore 6.5. After a joint venture last year the company is now renamed to CAMAO IDC GmbH. Since about 3 years I'm working there as a Sitecore Solution Architect and was responsible for many huge and exciting Sitecore solutions. Last year I was almost on every Sitecore Usergroup Germany as a speaker and presented some really cool topics.
The Email Preference Center was introduced in Sitecore 9.1, which was a significant feature added to the out of the box capabilities of Sitecore. But, the preference center is only available if you already got a newsletter. There is no clean and proper way to subscribe to those marketing categories. The idea was to create a custom Sitecore Forms field which allows to choose a manager root and displays the marketing categories which are associated to it. It also allows to choose a contactlist to which the contact should be subscribed to allow double-opt-in. The sample subscription form acts like the prefrence center itself.