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://camel.apache.org/maven/current/camel-spring/apidocs/) also used by the Camel Maven Plugin.
The starting guide is a good place to start:
And the concrete walk through a plain old java main example:
Walk through an Example
The FAQ have some more details:
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.