Since I'm eager to learn the latest technologies behind the 'cool' web apps, lately I've been researching about large AND relatively cutting edge open source web apps in the wild, not necessarily commercial.

One striking example that I've found (here at HN) was NewsBlur: https://github.com/samuelclay/NewsBlur (massive cudos to Samuel Clay for open sourcing it)

The technologies involved in making NewsBlur tick are pretty much in sync with what I plan to learn (I'll try installing and debugging it at my VPS) but I'm curious of other such open sourced projects that you know of.

Your turn,

Cheers