Thanks I found this list very helpful so did a quick check on the tech of some of them:

1. Spree: headless ecommerce with REST/GraphQL APIs built using Rails/Ruby. Next.js and Vue starter sites

2. Saleor: headless ecommerce with GraphQL API built using Django/Python. Next.js starter site

3. Reaction/Open Commerce: headless ecommerce with GraphQL API built using Node.js/Javascript

4. Solidus: headless ecommerce with REST API built using Rails/Ruby

5. Medusa: headless ecommerce with REST API built using Node.js/Express/Javascript. Gatsby and Next.js starter sites

6. Sylius: ecommerce built using Symfony/PHP

7. Shuup: ecommerce built using Django/Python. Looks like open source version is dead

8. Vendure: headless ecommerce with GraphQL API built using Node.js/Typescript