Top 3 Open Source ASP.NET Core based e-commerce web applications
Listed below are top 3 open sources, cross-platform ASP.NET Core based e-commerce web applications

nopCommerce

nopCommerce is the best open-source e-commerce shopping cart. nopCommerce is available for free. Today it’s the best and most popular ASP.NET e-commerce software. It has been downloaded more than 1.8 million times!
nopCommerce is a fully customizable shopping cart. It’s stable and highly usable. nopCommerce is an open source e-commerce solution that is ASP.NET Core based with an MS SQL 2008 (or higher) backend database. There are several plugins also available.

Site — https://www.nopcommerce.com/
GitHub Link — https://github.com/nopSolutions/nopCommerce

SimplCommerce

A simple, cross-platform, scalable, modularized e-commerce system built on .NET Core. This application is based on Micro Service Architecture.

Site — http://www.simplcommerce.com/
GitHub Link — https://github.com/simplcommerce/SimplCommerce

grandnode (Powered By nopCommerce)

It’s an open-source, free, cross-platform e-commerce software based on ASP.NET Core 2.2 and MongoDB — NoSQL database. You can run it on Linux, Windows, and macOS easily. GrandNode also supports Docker, so you are able to install it just in seconds with Docker.
It can be used for any kind of online store. GrandNode is a perfect choice for people who want to sell simple products. It’s a solution dedicated to the most demanding users. You can also create auctions, booking/reservation products or product kits. GrandNode became a mature solution especially for developers who want to develop a modern, functional and high-performance e-commerce system.

Site — https://www.grandnode.com/
GitHub Link — https://github.com/grandnode/grandnode

This open-source e-commerce web applications are great to get started. You can also check out their source codes for a good reference of real-time scalable applications.