Scanx0r 

This app uses QRCodes for both worker registration and inventory item redemption for small to medium-scale events. It does require a backend server capable of running Perl and Apache. It also requires system administrator capable of following simple instructions and capable of obtaining an SSL cert signed by a trusted CA

Dagmar d'Surreal is the developer of the tool which relates to the Events category. This application was downloaded and set up by over 5 users and its latest stable update was on Nov 4, 2016. Users rated the app 4.6 on Google Play.

Download the installation package of Scanx0r that is free of charge and take a look at users' reviews on Droid Informer. The app is totally safe to download.