It seems that the license not MIT or GPL. The Git repository is here

https://github.com/ServiceStack/CreatorKit.

The deployment also seems rather complicated for just a UI that would use something like SES in the background.

https://github.com/ServiceStack/CreatorKit/blob/main/.deploy...

I use Listmonk and I have no complaints, it's simple and does what it promises

website: https://listmonk.app/

repo: https://github.com/knadh/listmonk