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Chef is cross-platform. Offering support for the biggest platforms out there: Linux, Windows and *nix.
Pro Popular choice among large companies
Chef has an impressive list of companies using it's automation service. Among them is Facebook, Etsy, Ancestry.com, PharmMD and Yahoo.
Pro Large community
Chef has a relatively large community. One of the reasons for it is the fact that it's a pretty old and mature tool. Chef, originally released in 2009, is a more mature product. Being popular and with a large and dedicated community means that Chef has lots and lots of resources and guides from third party sources out there for beginners to pick up. Not only that, there are also many plugins and configuration recipes made by the community.
Pro Strong version control capabilities
Chef is centered around Git for it's configuration and deployments. Because of this, Chef also has great version control capabilities through Git.
Chef was released in 2009, which is relatively a long time ago for software. Since then it has been through several versions and many bug fixes and tests. All of this can make Chef more appealing to teams who are looking for stability and maturity, which are things that Chef brings on the table.
Con Ties you to Ruby
Chef is written in Ruby and its CLI uses a Ruby-based DSL. In order to fully use and customize it you need to use Ruby as Chef does not give users any other choice when it comes to languages to use to configure it.
Con Steep learning curve
Chef has a steeper learning curve than many of its competitors, making it a more difficult tool for the non-devs of a team (such as sysadmins) to work with. For some teams, the added cost of teaching Chef to the team may outweigh the benefits.