Apps on GitHub extend and improve existing workflows. People can build apps, purchase them from GitHub Marketplace, or browse useful tools and services that integrate with GitHub in Works with GitHub.
Note: GitHub Services will no longer be supported as of October 1, 2018. Please see the blog post for details. You can use the Replacing GitHub Services guide to help you update your services to webhooks.
For a walkthrough of the process of building a GitHub App, see "Building Your First GitHub App."
GitHub Apps: Use the GitHub Platform Forum for support requests, bug reports, and discussions. The forum allows you to collaborate with other integrators as well as engineers and product managers from GitHub.
OAuth Apps: Contact GitHub support directly.