Large distributed research network
You're probably thinking of PlanetLab.


  PlanetLab is a global research network that supports the development of new network services. Since the beginning of 2003, more than 1,000 researchers at top academic institutions and industrial research labs have used PlanetLab to develop new technologies for distributed storage, network mapping, peer-to-peer systems, distributed hash tables, and query processing.
  
  PlanetLab currently consists of 1335 nodes at 645 sites.


More generally, there are lots of "testbeds" (as these networks of distributed resources are called), including Emulab, PlanetLab, ORBIT, DETER, Seattle, and many others. Each has various advantages and disadvantages, depending on what you're trying to do. These are often federated so that users can access resources from multiple testbeds; projects like GENI and FIRE are federations of testbeds.