All ERPs should have an API so you'd be able to integrate it with Shopify.
Anyone with the need for an ERP will have some very specific requirements so this can vastly effect the development time (and costs) of that integration.
This post might help in your thinking process:
Hi Jay! I`ve used for a while EasyERP it seemed like good and quite interesting ERP, and looks like they`re going to launch some kind of direct integration with Shopify and other platforms (if you can trust those guys from support =)) ). Seen it here https://easyerp.com/. And, yeah, it`s opensource.