Since ColdFusion is itself Java-based, I would imagine it's not too much of a stretch to suggest that CFML code could be deployed on Google App Engine.
Blue Dragon is a commercial solution for deploying CFML code on Java servers.
Are there any open source alternatives that could be used for App Engine?
It's described in this thread how someone got OpenBD (Blue Dragon) running on App Engine:
Are there any open source alternatives that could be used for App Engine?
Railo is another obvious candidate here, and some people appear to be trying to tweak it for use on Google App Engine.
Check out http://www.stax.net/ - Stax networks made by a former Allaire(r)?
Works great, supports coldfusion out of the ..cloud. You download a precompiled source file, put your stuff in, upload it and it all works, no fighting with it.
I know google app engine is quite restrictive, it will involve opening up the source and removing everything that attempts to write to the file system, and changing your database interaction.
You can checkout this thread and group as a resource for Open BlueDragon as well as the wiki. Looks like they have a branch already which is working towards GAE compatibility.
On the Railo side of the CFML open source pond you can reference this article from help compiling Railo on your own from the source.
Joining both of their respective google groups and asking questions should yield fruitful as well.
Good Luck!
I am putting together some demos that run on Open BlueDragon, which in turn is running on Google App Engine. The list is small at the moment, but eventually it should give you a good idea of what is opssible with OpenBD and GAE.
http://www.brighthub.com/hubfolio/matthew-casperson/blog/archive/2010/05/12/cold-fusion-demos.aspx