I'll ask the obvious question not in the FAQ: How is this different from MongoDB?
* A far more advanced query language -- distributed joins, subqueries, etc. -- almost anything you can do in SQL you can do in RethinkDB
* MVCC -- which means you can run analytics on your realtime system without locking up
* All queries are fully parallelized -- the compiler takes the query, breaks it up, distributes it, runs it in parallel, and gives you the results
But beyond that, details matter. Database system differ on what they make easy, not what they make possible. We spent an enormous amount of time on building the low-level architecture and working on a seamless user experience. If you play with the product, I think you'll see these differences right away.
Note: rethink is a new product, so it'll inevitably have quirks. We'll fix all the bugs as quickly as we can, but it'll take a few months to iron things out that didn't come up in testing.