Android APK file is available on the Releases page. Download the APK file and install it on your Android device.
Windows client can be built from scratch. Simply pull the code and build.
IOS is not currently enabled as I don't have an IOS device to test on. If you have an IOS device and would like to test, please let me know and I will enable the IOS build.
No API credentials or app registration required. On first launch, tap the profile button and log in through the Reddit login page. Your session is saved automatically.