Cω (pronounce C omega and usually written as "Cw" or "Comega language") is a free extension to the C# programming language, developed by the WebData team in SQL Server in collaboration with Microsoft Research in the UK and Redmond. It was formerly known as the codenames "X#" (X Sharp) and "Xen". It was renamed Cω after Polyphonic C#, another research language based on Join calculus, was integrated into it.