Hi @ghfan Thanks for being part of the GitHub Community Forum!
GitHub Apps are the most powerful way to utilize GitHub’s expansive REST and GraphQL APIs. In addition to having access to most of the API endpoints available to developers, only GitHub Apps have access to the Checks API. GitHub Apps also have granular permissions that allow apps access to only what they need, which is an advantage over OAuth apps. For examples of smaller apps, you can check out Probot apps. For examples of larger scale apps, check out GitHub Marketplace!
I hope this helps!