MongoDB is a classic example of the innovator's dilemma. In its first incarnation it had no ACID transactions, no joins, no Geo-Spatial indexes, no inverted ind

MongoDB is a classic example of the innovator's dilemma. In its first incarnation it had no ACID transactions, no joins, no Geo-Spatial indexes, no inverted indexes, no SQL query language etc. What it did have (which no relational database had at the time) was JSON as a coin of the realm and a distributed database model. Run the clock forward and MongoDB now competes on equal footing with relational databases for all those features but it still has the key competitive advantages of JSON as a native format and a distributed architecture.