If you want to get funded by YC as a founder in the future, but you don't have a startup that's ready for that yet, joining the YC software team is a great hack to get there.
The YC software team is a small group of hackers in SF that write the software that makes all the parts of YC work.
As a member of the software team, you'll get full access to the YC program, just like founders do. You'll learn the ins and outs of how YC works, and you'll get to follow and learn from hundreds of companies. You'll meet the best people in the startup world and get exposed to the best startup ideas.
Software is how we can scale YC, and the limits of that are probably further out than most people think.
You can apply here: http://bit.ly/1Od0T2l.