People often use Infinispan in their business software and I think it will be pretty hard for you to find anything interesting. I ran a query through ohloh  and github search  but I didn't find anything interesting there.
How about helping Infinispan project? We have plenty of things to do . I might find you something more interesting if you tell me what parts are you particularly interested in?
Thanks Sebastian. I think I will play a bit with Infinispan in some playground to first learn the basics. At the moment I simply know too little about it to be helpful, I guess. I will come back once I feel a bit proficient with it.
also during learning by plaining with tutorials and quickstarts and reading the documentation feedback is highly appreciated. You migh correct the documentation or send comments on it, ot here in the forum.
This will be the first contribution and after a while you will are able to do more.