Top NoSQL Database Engines

I am not a fan of the term NoSQL. Many others are, however, and it has become a permanent part of the collective data storage nomenclature, meant to describe schema-less, non-relational data storage schemes. NoSQL is an umbrella term, one which encompasses a number of different technologies. These different technologies aren't even necessarily related in any way beyond the single defining characteristic of NoSQL: they are not relational in nature; for right or wrong, Structured Query Language (SQL) has become conflated with relational database management systems over the years. So, while I am not personally a fan of the term NoSQL, I can appreciate why others are, given that it quickly implies what it is we are talking about by explicitly stating what we are not talking about.