Whisper (http://whisper.sh - but download the app to see what it really is) - Santa Monica, CA - Use Erlang, Node, Ruby, Python, and Cassandra. Help us grow from 2.5 BILLION pageviews/month to 25 Billion. We're a team of 8 devs and need a lot more - in data science, functional programming, iOS and Android. Come work in a house two blocks from the beach. (Sequoia and Lightspeed funded) - chad@whisper.sh
Sorry for not elaborating on what it is. You have to download the app because the web is just a view on some of the content. It's an alternative, pseudo-anonymous social network with a LOT of users (though not generally the demographic on YC). It's not a meme site / image macro site at all - it's just hard to see what it is the same way it was hard for people to understand Twitter for a long time after it launched. (Is it a blogging site, is it an RSS replacement? etc)