PouchDB is a database written in JavaScript for web browsers that has in built sync capabilities.
For a long time 'web' was synonymous with 'online'. That is no longer the case, Mobile web usage is set to overtake desktop web usage shortly and a growing number of examples are showing that web technology is capable of handling the type of applications that were traditionally built using desktop native technology.
The new wave of offline web applications are going to need somewhere to store their data and they are going to need to learn how to move that data around as their user moves from device to device. How about we build a database with that functionality built in?