This is a online checkers game without any backend so it's not required. It works using webrtc. It's available both online on a browser (LINK: http://chief822.github.io/checkers) and on android (check github releases for app.apk). Both of these versions don't have TURN relay so may not work on certain networks.
do the usual install dependencies using npm install then run with npm run dev.
first cd into android directory cd android.
Next step is a bit hard. If you bulid conventionlly using ./gradlew assembleRelease then there always seems to be a problem in the apk that makes connection establishing using webrtc fail so currently doing this way.
Use the debug version of apk using npx cap run android. output is in android/app/build/outputs/apk/debug/app-debug.apk or maybe use ./gradlew assembleDebug i havn't tried it to confirm. You can check online to set up your environments to make these commands work.
Connection error:
First make sure you arent behind a restrictive NAT like symmetric NAT you can confirm with a free online tool like checkmynat otherwise switch to a different wifi.
Trying making the other way instead. For example if device A is making the first offer when connecting with device B, start with device B instead. This may work as certain devices have restrictive firewall like limited UDP ports which make direct webrtc connection difficult. If still not try with different devices