Warung mPOS is a micro point-of-sales for Android devices. Easy to use. No ads or whatever hidden fishes.
Also available freely (usually same version as here) in PlayStore. https://play.google.com/store/apps/details?id=com.haikal.warung
If you choose to download it from here, unzip the file and run the APK. Should be a straightforward installation.
Also, contact me at Facebook for any questions.
https://www.facebook.com/WarungMPos