A distributed computing project currently trying to take the RSA challenge of RC5-64, and also working on OGR-24 and 25 (Optimal Golomb Rulers). Previous projects included CSC and DES. http://www.distributed.net/
Prof. Chris Caldwell's database of virtually every large or otherwise interesting prime number known; includes the 5,000 largest known prime numbers and records for specific types. http://primes.utm.edu/
Primo, a primality proving program based on the ECPP algorithm. With Primo one can check crypto-primes and prove whether or not they are actually prime. http://www.ellipsa.net/
Attempt at factoring the huge Mersenne number 2^(2^61-1)-1. Software for Windows, DOS and Linux. Work reservation via email. http://www.ltkz.demon.co.uk/ar2/mm61.htm