app but used as library. addons can - be consumed by Ember apps - be wrapped over non-Ember javascript libraries - add preprocessors to the default registry, e.g. ember-cli-babel - be identified by keyword `ember-addon` in package.json
runs every time with parent app - hooks - isDevelopingAddon - helps while developing addon - included - import third party libraries. - locals - customising templates
- default blueprint - runs automatically along with `ember install addon-name` - can be run manually in case of addon upgrades - `ember generate addon-name` - other blueprint for extra functionality, need to run manually - `ember install blueprint-name`