Sysl (pronounced "sizzle") is a system specification language. Using Sysl, you can specify systems, endpoints, endpoint behaviour, data models and data transformations. The Sysl compiler automatically generates sequence diagrams, integrations, and other views and also offers a range of code generation options, all from a common Sysl spec. The set of outputs is open-ended and will grow to support other representations in future.
To make it easy to reuse Sysl across systems, the compiler translates Sysl files into an intermediate representation expressed as protocol buffer messages. Using the protoc compiler, users can easily consume Sysl models in their programming language of choice in a typesafe way without having to write a ton of mapping boilerplate.
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Sysl is currently targeted at early adopters. It is usable in anger, but has a ways to go in terms of usability, especially on the documentation front (as can be seen above).