Chef is a new open-source system integration, configuration management and provisioning application, released under the Apache 2.0 license by Opscode, in Seattle, Washington. Chef operates by defining system nodes, cookbooks for performing administrative tasks, and libraries for defining interactions with other tools such as applications, databases, and system administration resources like LDAP directories.
Chef is implemented as a Ruby-based DSL which is interpreted by Chef clients, working under the direction of a Chef server. Clients authenticate themselves to the server using OpenID, then synchronize the needed resources and libraries automatically. These resources are then used by the client to perform steps toward configuring the client node, a process called convergence. The ideal is that the configuration should be completed in one step; if it can't be, then the goal is for the client to make progress with later invocations in order to "converge" on the desired final state.
While Chef has just been announced, and is still an early version, it is being used in production in several installations.