Hosted R

I looked in the archives and couldn't find anything that really 
addressed my question so here it is -

Does anyone know of any web sites/environments that hosts R for free, 
web-based, multi-user access to the R engine. My apologies if the 
question is too simplistic for this forum. The reason I ask is that I'm 
looking at the possibility of establishing an R grid if one doesn't 
already exist, and if one does, then I'm looking for interfaces, 
protocols, and guidelines for adding an R node.

Matthew K. Hettinger, Enterprise Architect and Systemist
Mathet Consulting, Inc.