Stax Networks provides servlet hosting in the cloud. In a way it's like app engine but instead of "app engine apps" that use the special datastore, you deploy straight up servlets that use mysql databases you can create on demand. They have a nice graphical web-console. Each version you deploy gets tracked and you can roll back if you need to.
You can use JPA and whatever other frameworks you like. It's built on top of EC2, so you get fast access to any other AWS services you use. There is monitor that allows you to view application resource utilization and health, you can view all the logs. And you can have different environments like staging and production.
It's currently in beta test. I was approved for the beta test after a day or so.
The other question you reference is specifically about Python and AppEngine. You can't use Python on Stax Networks, although Jython and the other JVM languages are available like JRuby, coldfusion etc.