Mapton is written in Java and is based atop the NetBeans Platform (NBP).
Some of the main advantages of the NBP for Mapton is the Window system, the Plugin manager and the Lookup system.
NBP is based on the Swing GUI framework but Mapton is a hybrid using JavaFX where possible and Swing when necessary. In practice, Swing is used for top level windows and dialogs.
The source is hosted at github.com.