The UD stands for United Devices - it's a system of distributed computing for a variety of purposes. The
YaBB SE Team is dedicating their processing time to Cancer Research.
The idea is very simple (skip this part if you ever did SETI@Home - it's the same idea). You register and install the client on any number of PCs. When the client is running, it downloads data from the UD servers, then it uses idle clock cycles on your machine to process that data. When it's done - it sends the results back to the server.
It's great because there is minimal impact on your machine, but when you add up that little bit of processing from a large number of users - it can really make an impact.
Here is some information on the projectHere is where you can download the clientHere is a link to the YaBB SE Team informationYou register by installing and running the client. It walks you through the rest.