As Baldy18 said, it's using many "standard" desktop computers to do the work that couldn't be done by even the biggest Supercomputers.
For example, the
Seti @ home project breaks up radio signals recorded from a radio telescope and sends them out to the computers of over 3 million people who have signed up.
RC5 is a project to show that even by brute force the 64 bit encryption is strong enough to not be broken easily, and that nothing stronger is needed. The user who finds the hidden "key" (the code that decrypts the message) will win US$1000.
Folding @ home which studies protein folding, misfolding, aggregation, and related diseases.
Genome @ home is F@H's sister project at Stanford university, which studies genomes and what happens to them and errors and related diseases.
ECCp-109 looks at elliptic curve discrete log computation. Basically it looks for Distinguishing Points, and when two users uncover the same point, each will win US$1000
There are many other projects, but i can't think of any more and i will be late for college if i stay any longer
And, welcome to the Distributed Computing forum! I hope you enjoy your stay here and will become interested in any of these projects, and join our TeAm for the project you choose to do
Confused