Please follow these steps to install Gitabase application:

1. On your Android mobile device go to 'Settings', open Security section. Tick 'Unknown Sources' under device administration to allow installation of non Play Store apps.

2. Download .apk file of the Gitabase App.

3. If you open this website using your laptop/desktop computer, connect your mobile device to your computer using USB cable. Copy gitabase5.apk file to your mobile device using Windows/Mac file browser.

3. If you open this website using your mobile device, open file manager application on your mobile device, go to the 'Downloads' folder.

4. Open file manager application on your device, find gitabase5.apk file you copied and open it

5. Follow app's instructions to complete the installation

These steps are also described in this youtube video