Draw a card picks a random Draw a Box exercise to use as a warmup exercise. You can then rate how well the exercise went for you. Exercises you grow more proficient in will be selected less often. It is a variant on the Leitner flashcard system.
The settings page can be used to select the exercises you want included, and it allows you to override your proficiency level. It's also possible to add custom exercises in the mix.
It's important to note this site uses your browser's local storage. This means your progress and custom exercises will be lost upon clearing your browser's data, or simply when using a different browser. For this reason an import/export feature is coming soon™.
Issues and feature requests can be reported on Github.