No apps are officially created or endorsed by TFP. There were a few created by members that "should" match our recommendations, but no guarantee. Unfortunately, some of these members are no longer as active and may not be maintaining these apps.
With the pace and variety of mobile device of versioning, app dev is kinda a volume proposition these days.
You're way better off using a web-based interface when you can. With that said, I recall that pool math used to be available as a spreadsheet (or am I dreaming?) if so, and if we can dig it up, you'd be better off with an offline spreadsheet-reading app methinks
We don't have the resources for building an app at this time (unless you're offering ). It takes a lot of work to build an app because you need to be able to build one for both iOS as well as Android, deploy the app and then update as often as is necessary to make improvements, fix bugs, keep up with OS changes, etc, etc. That takes lots of time and time = $$$ . The donations we receive are just enough to keep the lights on and to refill the banana chip feeder we use to keep the site Admin fed....speaking of the Admin, I noticed the chains we have securing him in the basement are starting to rust a bit. Looks like we'll need to raise some funds for a new set of chains...maybe we can even get the padded neck collar too...
I concur re: the issue of maintaining an app...however, I wonder if folks who wanted it were to take the spreadsheet I linked to and convert it on a google drive account it would be accessible to them on any device provided they're using google drive mobile interfaces, etc.
The web app I made linked above does all the calculations you need in it and logs your chemicals. I am adding stuff daily and have been for 2 months. It works great in all mobile browsers for easy development and cross compatibility. If people eventually want it app form, I can do that but it won't be that much different. Go try it out! Poollogger.com