all by SUBSCRIPTION - no more BUY IT ONCE
1. You pay your one time fee for software that has been developed up to that point in time; or
2. You pay a subscription to have access to software that is continually updated.
Although, if you can constrain yourself to the limited board area of the free version you can always have access to the latest features anyway.
By the way, you only need to pay a subscription while you need access to the features of that subscription. If you need to develop a larger board for a few months, pay the subscription for just those few months then cancel it or drop back.