Ask HN: What problems can I process using distributed computing?

I am interested in building a small distributed computing network using JavaScript web-workers. What real-world problems are there that can be solved by such a network of multiple computers?

One example I could think of would be finding prime numbers: give the first node numbers 10000-19999, give the second node numbers 20000-29999, etc. But I think this doesn't really qualify as a real-world example. Any ideas?