a single location where open-source cluster and grid information can be aggregated and where community members can exchange information, experiences, and ideas related to the complete open source cluster software stack. In particular, but not exclusively, Grid.org provides a community where users of Cluster Express, and the various open source components it comprises, can interact with each other and with the source code.
I recall finding it frustrating that the URL "grid.org" (which I would have loved to have back when our Grid book first came out) was devoted to "desktop computing." But things sometimes come to those who wait!
For those interested in applying their home computers to philanthropic computing projects, I recommend the World Community Grid, which harnesses idle computers for useful purposes such as modeling potential AIDS and cancer drugs.