Unfortunately, mobile and web development are two separate things, and different companies/phones require different aspects to run an app. Logging on tg on your phone is probably the closest you'll get to a mobile app for the site, which to be fair, isn't horrible, but there's no reason to develop a mobile app if it doesn't introduce any significant new features.
I do think this would be a good idea to get new users to the site, however there would need to be quite a major overhaul of the site for it to work, as dustin24688642 said this site is quite outdated, plus the challenges would need to be more mobile friendly if that were to be a realistic option.
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