I've been looking at Rietveld as a solution for the lack of code reviews at my company. Can it be set up on a server in-house without using App Engine? It seems to have a bit of App Engine specific code, and I'm not sure it could be set up on a plain old Django/Apache install. I've looked around, but haven't found any information about this.
What about using one of these projects that provide the same backend services as GAE?
There may be more, these are just the ones I know about off the top of my head.
A bit of App Engine specific code? It's supposed to be an example App Engine app, so yeah it's pretty well tied to it. But, you're right, it does use Django which could make it somewhat more feasible to port. I'll second @cope360 recommendation, but from the sounds of your question, it doesn't sound like you've done much with App Engine. If it's only used by a few people, try running it on the GAE SDK itself.
Beyond that, I'd think you could take most of the code in the "codereview" directory and build you're own Django/apache app from that.
Rather than fussing around with a port or other GAE emulation, I would consider using ReviewBoard.
Review Board is a powerful web-based code review tool that offers developers an easy way to handle code reviews. It scales well from small projects to large companies and offers a variety of tools to take much of the stress and time out of the code review process.
For too long, code reviews have been too much of a chore. This is largely due to the lack of quality tools available, leaving developers to resort to e-mail and bug tracker-based solutions.
We've seen a lot of time and energy wasted doing code reviews both in open source projects and at companies. In both cases, code reviews were typically done over e-mail. A significant amount of time was spent in forming review requests, switching between the diff and the e-mail, and trying to understand what parts of the code the reviewer was referring to.
So in an effort to keep our sanity and improve the process both in our open source projects and at companies, we wrote Review Board. We hope it will be useful to your team too so you can focus on what's important: writing great products.