Successful small and medium businesses usually have several sales channels. If you want to have a stable business model, consider improving the variety of your sales channels. There are three main types of channels: offline store or business (brick and mortar), e-commerce, and online marketplaces. 

There are different types of data that retailers need to synchronize between selling tools of different channels: orders, reports, inventory, and customer information. 
Orders - you have to receive and process orders and sales from different channels. 
Reports - you need to have consolidated sales data, that allows you to see statistics as a whole and the sales by different channels to evaluate their effectiveness.
Inventory - you need to update the inventory changes of your products from different sales, as well as to manage to order and receive products. This will prevent selling products that you do not have in stock.
Customers - you have to identify your customers and track their purchases from different channels. 

We composed the list of online cloud-based platforms that can help businesses to manage multichannel sales. 

Before choosing some platform, you need to have a list of your current sales channels, as well as a potential one that you will open in the future. Check if some platform has an affordable way of integration with your sales channels. Find out if the possible platform provides you with synchronization of data that you need to manage your retail business successfully. 

TradeGecko

TradeGecko is a Singapore based software-as-a-service company that develops online inventory and order management software. TradeGecko has integration with the popular e-commerce platforms and marketplaces, as well as shipping and accounting platforms. It can synchronize orders and inventory to prevent overselling. TradeGecko also allows selling internationally with multiple currencies and has warehouse management features that assist in the management of inventory movement within a warehouse.

EasyEcom

EasyEcom is an inventory management solution for retailers with Indian origins that provides control over channels such as eCommerce, physical stores, wholesale, etc. The platform has integrations with major eCommerce and marketplaces like Amazon as well as ERPs. EasyEcom provides a central order management system and inventory management for multichannel sales.

Stitch Labs

Stitch Labs is a service developed by the company from San Francisco, USA. Stitch operations software streamlines retail operations management such as purchasing, inventory management, order management, fulfillment, and reporting. 
Stitch Labs has integrations with a few popular e-commerce platforms, market places, and POS. You can also integrate it with accounting, B2B wholesale, and logistic software.

Unleashed Software

Unleashed Software is a New Zealand-based software-as-a-service company that provides cloud-based inventory management. It has integrations with popular e-commerce platforms and the Amazon marketplace. The service also has alliances with many other software: accounting, CRM, and analytics. Unleashed includes B2B eCommerce Store and Unleashed Sales App that works in synchronization with cloud-based service and allows making sales and managing customers, products, and orders on the road.

Zoho Inventory

Zoho Inventory developed by an Indian-base company is an inventory management software.
Zoho has a suite of software that covers many business needs: accounting, analytics, CRM, help desk, project manager, and much more. Integration with them can significantly extend the functionality of the Zoho Inventory. Besides, the service has integration with other popular marketplace services (Amazon, eBay, Etsy), eCommerce platforms, as well as other services. Zoho inventory can consolidate sales from multiple channels by managing orders and adjusting inventory quantities across all channels.

Anchanto

SelluSeller from Anchanto, a company with HQ in Singapore and offices in the Asia Pacific region, is a SaaS-based platform that enables businesses to manage their ‘end-to-end’ eCommerce operations across multiple channels. SelluSeller Anchanto has Wareo - a platform for managing warehouses. SelluSeller can manage multichannel sales and has integrations with many popular marketplaces and e-commerce platforms. The service has inventory/stock and order management functionality that can consolidate orders and stock from multiple channels & regions synced to one platform.