During the RC5-56 contest there were two other groups (Cyberian and Infinite Monkeys) competing against distributed.net (it was called the Bovine project back then).

However, the RC5-64 contest is a much tougher problem (256 times tougher to be exact). We are not aware of any other competing groups that took part in the challenge of breaking RC5-64. Cyberian did announce early in the contest they would also be mounting an effort but never did so.

Finally, there were several similar efforts which took part in the first Secret-Key Challenge contest which had to do with DES encryption instead of RC5. The largest of these were SolNET and DESCHALL. (The DESCHALL group went on to win that contest in June of 1997).