From the about page
Riesel Sieve is a distributed effort to prove the Riesel conjecture by removing prime candidates for the remaining 101 85 K from over 11 million k/n pairs.

Individual sieving efforts per single K can take months to reach a sufficient level. This coordinated effort will allow us to sieve 100 times deeper and much quicker. No more sieving to 3T and then stopping in frustration as the hours per factor mount, now we can go to 300T and beyond.

For people doing PRP work on the Riesel problem, we plan in the future to do a distributed proth testing on the remaining k/n pairs. We have many K's reserved in our name, however we only intend to gather more when others run out of resources to find a prime at n=1million+ and join the project voluntarily. Noting this, we will not step on the toes of any current prp/proth tester by trying to do distributed proth testing at this time. We will wait until everyone has volunteered to come over.

Also, any current K reserver that would like to extend their current range to test is more than welcome to pick up a presieved range from us. You save weeks of hard work since we've already done the sieving. All we ask in return is two things: We'd like to have your residuals when you complete the range and we'd also like your help on sieving.