Shopify Marketplace Connect

I've been using this app for a couple of months now. It was easy to setup, and any questions I had were answered by support very quickly, even on a Saturday, which was very impressive. I use it to connect eBay and Amazon with my Shopify store. Stock is kept in sync across all platforms and my orders all come into Shopify for easy processing. A great app, if you need to do this in your store.