Dynamics 365 AppSource applications currently come in the following three flavors:

• Utilities/solutions installed straight to your instance with no external dependencies
• Solutions that are complemented by an external website, offered as a self-provisioned SaaS
• Solutions that are complemented by an external website but require the vendor's intervention to install an end-to-end functioning product

If you are planning on submitting an application to AppSource, you'll have to demonstrate that your solution follows a high level of quality. Currently, Microsoft goes through a very rigorous set of inspections for each app submitted. First, the app must meet the review guidelines published in the following PDF at https://smp-cdn-prod.azureedge.net/documents/AppsourceGuidelines/Microsoft%20AppSource%20app%20review%20guidelines.pdf. The code is then reviewed to ensure that best practices are followed, including a security review.

Microsoft may contact you to ensure that you are willing to support the application on all current Dynamics 365/Online versions (not all subscriptions would be using the latest version) and that you are willing to upgrade your app as new versions of Dynamics 365 are released. All these gates are there to ensure that AppSource hosts high quality supported solutions that will safely work on your current Dynamics 365 instance, as well as future versions.