Hello Tomasz,
QaA is our internal custom solution build on Kentico there are used out-of-the-box web parts like Forms, Repeaters, Data Sources, etc.
But the logic is implemented in this way:
1. Questions are custom page types
2. Answers are stored in the Custom table, linked to Question based on the NodeID
3. The rest is handled by our custom WCF service which is using Kentico API and JavaScript
Best regards, Martin