Hi Guys,
you may have been looking for a way to have your items both on Shopify and other marketplaces at the same time (eBay, Amazon, Etsy to name a few), without risking to double sales and possibly listing only once.
We are a San Francisco based startup and we just released Nembol: https://apps.shopify.com/nembol
It's completely free, give it a try and let me know your thoughts.
We are constantly looking for ways to improve.
Thank you,
Simona