Rails SaaS Boilerplates and Starterkits. Trying out Bullettrain for the first time

Sometimes I have a "new genious app" idea, but when I start coding it I get demotivated with re-creating all the same functionality for the 100th time:
Authentication, SSO
Teams and Multitenancy
Roles (Authorization)
Payments & Subscriptions
Responsive layout
UI elements
Internationalization
CI setup
Tests for all the basic functionality
These days there are many starter kits.
I will try to make a general overveiw and comparison.
I will also try using and understanding the recently open sourced Bullettrain SaaS template, that I have high hopes for!