Ninja can easily be extended by modules. This page contains popular modules available for Ninja. Usually the linked pages contain a short description how to setup stuff:
Undertow standalone - alternative to Jetty
Template Engines —————-
Rythm templates
Mustache templates
Jade4Ninja (Jade) templates
Rocker templates
Pebble templates
EBean RDBMS ORM support (for EBean versions <= 7.2.3)
EBean RDBMS ORM support (for EBean versions > 7.2.3)
MongoDB/Morphia Integration
Activity support - light-weight workflow and Business Process Management (BPM)
Camunda BPMN Integration - Camunda Workflow, Business Process, and Decision Management