OFF System stands for Owner Free Filing System, and it is a P2P system with a bit of a tweest.
No copyrighted data is transferred to your peers, at all.
Instead, what they do is if you share a file, the program creates a bunch of segments that are 128kb long that only contain randomized data, and creates a key that, by XOR-ing, retrieves the original.
The blocks of totally random data is then dispersed on the network, along with the key.
None of these hold anything that is copyrightable.
When the blocks are downloaded and reassembled with the key, the original content can be received.
However, the totally random pices of information can, with other keys, be used to assemble other content as well.
Think of it this way, say the RIAA owns the number 12.
But they don't own the number 5 or 7, so what if I add 5 and 7, do they own the formula "5 + 7"? Of course not, and if they did, what does the sequence "5, 7" really mean?
The bottom line is that it is possible to share anything without the need for cryptography or other forms of obfuscation, because there is nothing illegal taking place.
There are just a bunch of computers that trade completely randomized data with each other.
The trade off is the overhead. You have to store a bit of data, and downloading goes slower than on direct file transfer.
On the other hand, the same stored data can be used to restore many different files, and until you give the program the command of restoring something, it is simply not there, thus if you would get caught, you'd only have a hard drive full of meaningless data.
Also, on the other hand, in contrast with most other p2p services, like even the best anonymous ones, this one actually works!