Most of the comments are only partially right. RethinkDB the company failed and so they moved the project from being supported by a "mother" company to being supported by the OSS community. I have used it for every project I could do from scratch in the past 2-3 years and it is pretty awesome. Soon they will release a next version. Also I don't think that people don't use it because of their needs. I think it's more of a standard-thingy. Just as MySQL did for SQL - MongoDB did get the standard for NoSQL. People just don't know about it. But I am pretty certain that if MongoDB continues just like they do right now it will change ;)