Working Copy is a Git client for iPad and iPhone. Because Ulysses allows embedding external folders on iOS, the two apps integrate nicely.
Git is a popular version control system for projects where several people work with the same files. While it is mainly designed to coordinate work during software development, it can also be used to keep track of changes in any set of files, e.g. in technical documentation or manuals. Projects in Git are called repositories, and each person working on a project has a copy on their device. The collected work is stored in a shared remote repository on a version control hosting service such as GitHub.
Working Copy allows you to clone your Git repositories onto your mobile device. It integrates nicely with Ulysses on iOS without needing to copy anything between the apps. While Working Copy manages Git repositories and makes them available in the Files app, you can edit contained text or Markdown files with Ulysses.