Is it possible to use the Overwolf API to create an app for my personal use only? How would I go about doing that?
Yes, you can create an app for your personal use!
You would go about it as you do with any Overwolf project - send us you app proposal (Submitting an App Proposal | Overwolf) and mention your plans for this app and what it will require. Once whitelisted, you will get access to our dev tools and can start working.
Do note that while we allow the use of our API for private purposes, apps that serve all our users are our main focus and so as a private app dev you will have to be more independent and self-serving.
Good luck with your app!