The FOSS app I was using to manage my flash cards was great, but locked to the platform I was using. I whipped this up over a weekend to use instead from any platform, and kept it easy to update when needed. You can see it in action here: https://flashcards.devlay.com
Run ng serve for a dev server. Navigate to http://localhost:4200/. The application will automatically reload if you change any of the source files.