Time-to-Page is a calculator that converts listened audiobook time to the equivalent page in the physical book and vice-versa. It was originally built very simply and barebones, but I re-wrote it in React, Redux, and Bootstrap to show my skills in those technologies while also adding some extra features to make it a little bit nicer to use like saving book settings and measuring by percent completion in addition to time and page number.
This app is second most used that I have made with at least 2 visitors per day without fail since it has been online, and it is mostly accessed via Google searches! It turns out that this is a tool that people have needed, and in at least one case, it has been used as the main tool for calculating page number in a reading challenge on GoodReads!
It is built with React, Redux, and Bootstrap, and it is open source on GitHub.