Camel-core is the basic module of apache camel. It contains the public API and the Java DSL and several implementation packages.
The most important packages are:
builder
model
Contains the classes (*Type) that form the java DSL. The central class is the RouteBuilder
component
Some simple components like bean or log. You will find most components in the other camel modules
impl - implementation
Implementation classes for model and camel
processor
Definitions and implementations of many EAI patterns
spi - service provider interfaces
Interfaces to add plugins to maven like the TypeRegistry or Lifecycle
camel
Base package for camel. Defintions like Message and CamelContext can be found there.