Robust open source Node.js based projects for learning?

I'm working on learning particular node.js (specifically tower.js). I'd like to see some very robust open source application examples that revolve around more complex scenarios, particularly in the mapping area. I've not found a solid example as of yet that I feel I can sink my teeth into, but I'm hoping someone may point me towards a Google Maps or Open MapQuest style application that's built atop node if possible.

Any suggestions in this vein? Any robust example app is fine, simply one of those scenarios would be much more apropos.

javascript
node.js
towerjs

I've been working on an Open MapQuest based application on Node.js myself. This is the best full-stack reference I could find: Node.js, Express, Leaflet, PostGIS. But it's far from robust; in fact, it's vulnerable to SQL injection!

In general, you'll need two things:

a client-side map renderer like Leaflet, which is incredibly awesome.
a geospatial database like MongoDB, which has builtin geospatial indexing and which I'm using, or PostGIS which they used in that tutorial.

Then, just follow a Tower tutorial, and create a RESTful endpoint that queries nearby items of interest given a longitude and latitude. You probably won't be able to use Tower Models, since they don't support geospatial queries AFAIK. On the client side, check if your map's been moved, and fetch the endpoint to update nearby items.