JoeLister - Crosslist and sell Amazon FBA/FBM inventory to eBay & Shopify in minutes. JoeLister handles Automated Fulfillment, Quantity Sync, Listing Creation, and much more. Try for free.
SellerCloud - SellerCloud is a multi-channel inventory and order management system.
ecomdash - An easy-to-use inventory management software enabling small business to automatically sync inventory across sales channels - from one centralized software (SaaS).
Sellbrite - Multichannel ecommerce management for serious sellers.
inkFrog - Easily create listings using the inkFrog one-page-lister. Catalog auto-suggest makes it easy to match your product with eBay's catalog
3DSellers - Experience the ultimate eBay selling manager: all the eBay selling tools you need, such as an eBay listing designer, eBay listing tool & inventory manager, multichannel helpdesk, eBay feedback reminder, and many more eBay seller apps and features.