High performance and/or real time java open source applications [closed]

Question

Which open source java projects do you know to be high performance or real time performance? I tried hard to find them on github or google, but couldn't find suitable.
I want to learn from this projects, so will not be as a newbie on my interviews ;)
So far I am going to stick to Play Framework project. Are there better options?

P.S. I've seen possible duplicate, but I am looking for a very load intensive applications. As people in Deutsche Bank write.