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 ( also used by the Camel Maven Plugin.

The starting guide is a good place to start:
Getting Started

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.