Is it possible to start Camel as a standalone application, without embedding it in another application?
Yes Camel can run standalone or in any container. Running Standalone is as simple just to create a CamelContext, add routes and start it. If you don't want to write your own java main, you could use the one from camel-spring (http://activemq.apache.org/camel/maven/camel-spring/apidocs/) also used by the Camel Maven Plugin.
The starting guide is a good place to start:
Getting Started
And the concrete walk through a plain old java main example:
Walk through an Example
The FAQ have some more details:
Faq
And if you use Maven for your projects Camel has maven tools to boot up in standalone mode and quickly run you Camel application:
Camel Maven Plugin
This is how you can run the Examples that is included in the Camel distribution.
In Camel 1.4 we will also have ANT build.xml files to quickly start the examples standalone.