What's the simplest way to provide a portable, locally running webservice server application?

Question

We have a large website running that offers a JsonRpc web service.

For offline demonstration purposes, I want to realize a portable, locally running webserver with a minimalistic feature replication of the live webservice, and bundle this together with Html files which do Ajax requests to it. This local server executable should have as little dependencies as possible.

It's going to be run and presented by non-devs on non-dev Windows machines, so I would prefer having a simple executable plus the service code. The language would need to be .NET, PHP or Java.

I'll need a small database behind which probably will be Sqlite.

It's important to say that, for reasons I won't get into here, we cannot use the original web service code, but we have to rewrite it new for the local demo server. This is why I want to put minimal effort in the local server tech.

An installer for distribution is not mandatory, it's okay to have a zip file with an executable in it which starts up the local webserver.

What would you recommend realizing these requirements?