Development stores are for Shopify account members who have created their store but have yet to choose a monthly plan with Shopify and/or BigCommerce.
During this time, their website is active, but not considered "live" to customers. This means that the customer has the freedom to work on their store - editing it and setting it up to the way they want it to be - without the public being able to access it while it's still in production.
Once the customer eventually chooses a monthly Shopify/BigCommerce plan, their store goes "live", at which time customers can begin viewing it and using it for their online shopping purchases.
Because we wish to aid our customers as best as possible while they work to set up their sites, Rewind is free for development stores.