I've been doing EDI (Electronic Document Interface) for about 2 decades now. In that time, I've personally written 3 different EDI frameworks, 2 in Delphi, and one in PHP, plus we're working on a node.js version. Our overall goal is to make it affordable for small and medium sized companies to do EDI.

EDI is by far the best way to exchange data between two companies. By the best, I mean the most robust. Yes, it's less technically challenging to use JSON API's or other means, but EDI is the best way to automate it. EDI has strict standards for all data, and detects missing or bad data, and aborts the data transfer when needed. Most API's fall short in the area of data integrity.

EDI Shack has some open-source software

If you are one of the tens of thousands of WooCommerce or Shopify store owners, EDI Shack will be able to set you up with a plugin which can be used to monitor your EDI systems, plus programs and/or daemons/services to automate the sending or receiving of data from your trading partners. Some of it is even Open Source and Free.

You can check out EDI Shack here