Get SHOWUP on your phone.
No app store. Scan the code, then add it to your home screen - it opens full-screen, with its own icon, just like any other app.
Scan the code with your phone's camera to open SHOWUP there.
Or open this on your phone's browser:
showup.us.com
iPhone
Open in Safari → Share → Add to Home Screen.
Android
Open in Chrome → tap Install when it appears, or use ⋮ → Install app.