Portable MongoDB?

I created NeDB - a pure Javascript database implementing the MongoDB API. It can be used as a Node.js module and in the browser and supports persistence.

It also supports indexes which make it much faster than databases who don't (e.g. TaffyDB and it seems to be the case for MongloDB as well)

Disclaimer: I just came across this and haven't tried it yet. MongloDB (https://github.com/Monglo/MongloDB) looks interesting. From my quick look it appears to be a MongoDB look alike interface that makes it easy to back with local storage or a cache and AJAX to a server side store. But as I say I have not tried it yet. The joys of random github finds.