It is possible to buy a different non-AGPL license to MongoDB -- https://www.mongodb.com/community/licensing. With RethinkDB it seems completely impossible to do so. I begged and pleaded: http://sagemath.blogspot.com/2016/10/rethinkdb-must-relicens.... I just spent most of my time during the last two months rewriting SageMathCloud to use PostgreSQL instead of RethinkDB, with the catalyst for doing this being the AGPL licensing and some concrete enterprise customers needing a completely non-GPL'd stack for SageMathCloud. Coming out of this rewrite, and back to PostgreSQL (which I've used off and on for decades), I'm very impressed by PostgreSQL today, and the LISTEN/NOTIFY functionality is a solid building block on which to build something like changefeeds (thanks to the many HN comments on previous stories about RethinkDB for pointing this out!).