NB is a free Android app developed by Brewalan Le Dru, designed to help users write French numbers correctly in letter form. The app provides assistance in determining when to use a "s" or a dash when writing out numbers.

The user interface of NB is simple and easy to navigate, with a clear and concise layout. The app is designed specifically for those who frequently write out French numbers and need a quick reference tool to ensure accuracy.

Overall, NB is a useful and practical app for anyone who needs to write out French numbers and wants to ensure that they are doing so correctly. It is a great addition to any writer's toolkit and is highly recommended for those in need of a reliable French number writing tool.