Ask HN: Looking to create a plugin marketplace for my webapp. Any advice

We have a fairly popular SaaS platform that operates within the marketing industry (think Mailchimp).

We are wanting to setup an app/plugin marketplace and allow third-party developers to build extensions and integrations. These would then be submitted into the marketplace and our customers can then choose to enable them in their accounts.

Before we scope this project and build it, I thought I would post to see if anyone has worked on this project previously and if there were any docs worth reading. As well, are there any third-party platforms that can be used to make the process more easier and efficient.