Newbie question, which version of ShipRush to download?

I'm using Fedex to ship and Quickbooks to bookkeep. Which version of ShipRush should I download? Or are they all the same thing?

FWIW, my current ecommerce cart is unsupported by ShipRush, but am soon planning to switch to either PrestaShop or BigCommerce.

Thanks in advance for any responses.