I'm little bit confused. Cashier uses Stripe and Stripe is extended by Spark? Or ... ?
And which of that is payment gateway and which is just a Laravel code to handle subscriptions? And am I'm missing some other popular Laravel solution in payments/subscriptions?
Cashier is a package to make handling Stripe-based subscriptions in a Laravel app a little easier.
Spark is a package that basically replicates the functionality of Stripe’s customer portal. You can use Spark to let your customers manage their profile, subscription plan, payment method, etc.