What is xAPI?
"xAPI is an eLearning specification that makes it possible to collect data about the wide range of experiences a person has within online and offline training activities. xAPI’s use of a shared format for both the receiving and sending of data makes xAPI an ideal tool for sharing learning between multiple systems." Source https://xapi.com/
For more information on xAPI it is recommended you read https://xapi.com/
xapiapps is designed to make it easy to add sophisticated learner activities to your xAPI solution. Every activity your learners interact with will send xAPI statements to a configured LRS (or more than one!).