We describe the use of a cluster as a generalized facility for development. A development facility is a system used primarily for testing and development activites while being operated reliably for many users. We are in the midst of a project to build and operate a large-scale development testbed. We discuss our motivation for using clusters in this way and compare the model to a classic computing facility. We describe our experiences and findings from the first phase of this project. Many of these observations are relevant to the design of standard clusters and to future development facilities.