Slava @ RethinkDB here. I am not able to get into details yet, but the short version is that the commercial entity behind RethinkDB is shutting down. We're working on continuity for the open-source project. Full announcement (and details) coming in a day or two.
To everyone who has used RethinkDB for free and now wants the product of the company to be released to open source for free use:
Don't you see this is self fulfilling?
Don't pay for databases, database companies close.
Or, you can take this as a cautionary tale, and consider paying reasonable, good companies for the technology they create. Not out of pity or charity, simply because you're getting value from the software created.