Hi Matti,
Review Board does support writing add-ons (we call them "extensions"), which can do most things you might need. It depends on what you're trying to do, but extensions run as Python code within the Review Board process, and can augment the product in many ways.
As David metnioned, we're not available right now for any new projects (probably won't be for a while), but if you'd like to give us a sense of what the idea is, we can let you know whether it's something already planned for a future release, or how you might go about it.
Christian